Reddit mentions of Cooler Master Devastator - LED Gaming Keyboard and Mouse Combo Bundle (Red Edition)

As configured by you (i7, 3TB HD, 4GB video card), the cost comes to $3099.00. I added in 16GB of memory over the stock 8 since that's pretty much standard for most builds, anymore.

5k Dell Monitor: $1,439.99

Retail i7-4790: $307.00

Gigabyte GA-Z97-HD3 Motherboard: $102.95

Crucial Ballistix Sport 16GB Kit: $66.99

Corsair Carbide SPEC-01 Mid Tower Case: $48.99

Silverstone Tek 500W 80+ Gold PSU: $79.99

EVGA GeForce GTX 960 4GB Video Card: $229.99

CM Storm Devastator KB/Mouse Combo: $29.99

Total Cost: $2305.89

Video card was a bit of a toughie since the iMac uses a notebook GPU, so I went with something a bit faster, but comparable. This is a complete system with comparable to better specs.

Given the price difference, may as well go with a 980Ti for that extra graphics oomph or tack on some water cooling.

Edit: Woops! Forgot storage and OS!

WD Blue 3TB HD: $98.70

Samsung 850 EVO 120GB (configured as cache drive): $66.99

Windows 10 Home: $119.00

Revised Total: $2590.58. Still cheaper and could still sub out the 960 for a 980Ti and be under cost.

Congratulations! By the way if you are going to use the logitech keyboard may I suggest this from cooler master if budget is an issue. Or are you upgrading later?

Here are a few.

http://www.amazon.com/CM-Storm-Devastator-Gaming-Keyboard/dp/B00LZVP71A/ref=lp_1194464_1_15/184-6333544-3835912?s=pc&ie=UTF8&qid=1451359741&sr=1-15

http://www.amazon.com/Bluefinger-Illuminated-Keyboard-Customized-Mousepad/dp/B012VLRH2Y/ref=sr_1_2?s=pc&ie=UTF8&qid=1451359761&sr=1-2&refinements=p_89%3ABlueFinger

http://www.amazon.com/Keyboard-Set-BlueFinger%C2%AE-Adjustable-BlueFinger%C2%AE-Customized/dp/B015Q0F3NM/ref=sr_1_3?s=pc&ie=UTF8&qid=1451359761&sr=1-3&refinements=p_89%3ABlueFinger

http://amzn.com/B00LZVP71A
That fits in perfectly for his budget. Probably the best deal you could find with $30. The CM Storm Devastator - LED Gaming Keyboard and Mouse Combo Bundle (Red Edition)

Cheaper 970 (cheaper then the 390) http://www.amazon.com.mx/gp/aw/d/B00NNXVPS2

Cheaper PSU don't need that much wattage http://www.amazon.com.mx/gp/aw/d/B00K85X23O/

Edit: CM Storm not a bad budget keyboard+mouse (but mouse is pretty much a paper weight recommend changing asap) http://www.amazon.com.mx/gp/aw/d/B00LZVP71A/

The Corsair K30 is pretty solid for around $50. If that's too much (or you still need a mouse as well) this Cooler Master set gets used a lot in budget builds and should fare decently.

Yup, This One

Something like this do the trick for now?

http://www.amazon.ca/Cooler-Master-Devastator-Led-Gaming-Keyboard/dp/B00LZVP71A/ref=sr_1_5?ie=UTF8&qid=1417417970&sr=8-5&keywords=mouse+and+keyboard

CM Storm Devastator combo (membrane) - $30

A solid wireless logitech membrane - $25

Inexpensive offbrand AULA mechanical using Kailh Blues, a chinese knockoff of cherry MX's -$40

A rosewill keyboard with ALPS switches, clicky :3 $50

Nice backlit Perixx board with Cherry MX blues. $80

Much past that and you're getting into name brand mechanicals that are fantastic, but expensive. These are just some decent keyboards for their respective prices.

edit: fixed formatting

the storm devastator bundle is pretty much the only thing that fits the bill, and it's pretty well-rated so it should serve you well

This one

http://www.amazon.com/CM-Storm-Devastator-Keyboard-Edition/dp/B00LZVP71A/ref=sr_1_1?ie=UTF8&qid=1416666891&sr=8-1&keywords=CM+storm+devastator

I usually recommend this CM Devastator bundle. Comes with red or blue backlights.

http://www.amazon.com/dp/B00LZVP71A/?tag=pcpapi-20

http://www.amazon.com/dp/B00DKXXAAQ/?tag=pcpapi-20

It's cheap, but it's designed for gaming and will tide you over till you can get a good mechanical keyboard and a nice mouse.

http://www.amazon.com/dp/B00LZVP71A/?tag=pcpapi-20

[Here you go!] (http://www.amazon.com/CM-Storm-Devastator-Keyboard-Edition/dp/B00LZVP71A)

The mouse is a bit shit, otherwise I'm surprised you could piece together a system like this for under 400$.

This is said to be pretty good value, mind its a KB+Mouse combination so you can drop your current keyboard from the list and just get this bundle. Mouse has more flexibility in DPI depending on what kind of playstyle do you want and the sensor is probably better as well.

Cooler Master Devastator (Red)

This isn't a plug in one USB that activates both but it's a decent combo for $30. The keyboard is a decent membrane keyboard with some tactile feel and it's backlit. As for the mouse, I'm a palm gripper and prefer bigger mice so this mouse is somewhat uncomfortable for me. Other than that the mouse works well for the games I've played (CS:GO, TF2, and Overwatch). If you have any questions about this combo I can answer them.

For a rubber-dome keyboard, probably something like http://www.amazon.com/CM-Storm-Devastator-Keyboard-Edition/dp/B00LZVP71A

You really should explain what game you're playing though. If you do twitching then you probably need to learn not to twitch.

Change the SSD. The Crucial MX100 is cheaper and better.

http://www.amazon.com/Crucial-MX100-adapter-Internal-CT256MX100SSD1/dp/B00KFAGCWK/ref=sr_1_1?ie=UTF8&qid=1411622882&sr=8-1&keywords=crucial+mx100+256gb

You could also get a Corsair CX600M for $20 cheaper and it'd be way more than enough to run the system. Or, an EVGA Supernova 750G2 for $15 cheaper.

http://www.newegg.com/Product/Product.aspx?Item=N82E16817139048&cm_re=cx600m-_-17-139-048-_-Product

http://www.newegg.com/Product/Product.aspx?Item=N82E16817438028

For the price I'd say the EVGA looks the best.

The case looks good. Another alternative if you want a lot more cooling is the Rosewill Blackhawk, but it looks more flashy and perhaps less refined.

http://www.newegg.com/Product/Product.aspx?Item=N82E16811147107

As for the keyboard, honestly I'd not even think about going with such a basic keyboard unless it was for a very budget build. You'll be better served by getting something like the CM Storm Devastator Mouse/Keyboard combo. The keyboard is available either Red or Blue backlit and is pretty good for typing because it has well-spaced keys and good key travel. The mouse has buttons for adjusting DPI on the fly and side buttons you can use while gaming. Even if you already have a better mouse, it'd work great as a backup.

http://www.amazon.com/gp/product/B00LZVP71A/ref=gno_cart_title_0?ie=UTF8&psc=1&smid=ATVPDKIKX0DER

The rest looks solid. Good luck!