Reddit mentions of Syba 4 Port SATA III PCI-e 2.0 x1 Controller Card Marvell 9215 Non-Raid with Low Profile Bracket SD-PEX40099

If you want something dead simple, something this would work just fine:

Syba SD-PEX40099 4 Port SATA III PCIe 2.0 x1 Controller Card https://www.amazon.com/dp/B01464550K/ref=cm_sw_r_cp_api_d4-XzbJDEYTR4

I actually use these in unRAID. These are not gonna be blazing fast SAS3 speeds capable of maxing out read performance across 4 disks all at the same time in a software raid environment but they will work perfectly well for what you described and are cheap!

Edit: I linked the 4 port as that's the one I use. You can go even cheaper and get a 2 port or go extreme and get a 10 port. For me, I don't run raid or use parity so as long as a given controller can max out my drive, that's all I need. It's not like we're running Plex servers full off 1TB M.2 drives :)

In the past I ran LSI SAS 9201-16E's in my JBOD rack chassis. I'm simplifying everything, going down to tower chassis with larger drives. No more SAS cards, cables, expanders.. I wanted less drives, less chassis, less complex.

I bought one with 24GB RAM and no hard drives for $299 from eBay back in 2015.

The one on Craigslist is overpriced, for sure. In fact, here's a hex-core Xeon with 12GB RAM for $189.99 (add $43.08 for shipping to a Denver zip code)- http://www.ebay.com/itm/Dell-T7500-CAD-PC-Xeon-6-Core-2-66GHz-X5650-12GB-RAM-/172642233077

For just under $500 (including shipping to Denver), you could build one with dual hex-core Xeons and 48GB RAM from the same eBay seller-http://www.ebay.com/itm/Build-Your-Own-Dell-Precision-T7500-12-Core-2-93GHz-X5670-No-OS-Wholesale-/382099410600

As far as the machine itself, I have a Xeon x5687 in mine and it's my daily driver (Windows 10). Plex only uses 1-3% CPU if it's not transcoding and I don't even notice it. I run VMWare Workstation 12 Pro and it doesn't break a sweat running multiple VMs at once, so I'm sure it would do fine running ESXI.

(Transcoding is another story due to the lack of cores, which is why I converted all my media to x264/AAC for playback on a Roku 3. I've since upgraded to the Nvidia Shield and haven't come across a file yet that requires transcoding. There's definitely better CPUs out there for transcoding, but it would be an upgrade to your NUC. If you did the dual 6-cores, it would do really well, I think.)

It's not a terrible machine by any means. Keep in mind the tower is huge though. I use an old Samsung 32 inch 720p TV as one of my monitors and it is taller than that.

It runs pretty quiet but I did install SpeedFan so I could manually ramp up the fans when doing CPU intensive stuff such as video conversion (SpeedFan didn't detect the fans until I went into options and clicked a box that says "Enable DELL support (use this function only on DELL notebooks)". After checking that, clicking OK, and closing/relaunching SpeedFan, it detected the fans and allowed me to control them).

You can install a very cheap storage controller and plug it into 1 of the PCIe slots for SATA III capability. I've got an 8TB drive and my 1TB SSD connected to a cheap (under $30 new) Syba card- https://www.amazon.com/Syba-SD-PEX40099-Port-SATA-Controller/dp/B01464550K (If you decide to go this route, you will need to install Windows on an SSD using the onboard controller, install the drivers for the card, and then disconnect/reconnect the drive to the PCIe Sata card. Not sure on how that card would work with ESXI, though.)

I filled the onboard controller with 3 X 2TB refurbished HGST Enterprise drives off eBay that sold for $40 each back in 2015 and have 15TB total storage. Not including the SSD and a 750TI I slapped in for light gaming capability, I spent under $650 for 24GB RAM and 14TB of storage.

Would be even cheaper today, especially with the used workstations with E5v2 Xeons hitting eBay now. Don't spend $400 on this one.

If all you want is a 4-port SATA card that will only take a PCIe x1 slot, look for something like this Syba card.

Now, going with a PCIe x1 slot is going to bottleneck you a little - max speed is 500MB/sec, and a 7.2k drive can usually give you upwards of 150MB/sec, so four of those could see some slowdown, but overall there won't be a ton.

That being said, if you've got the room for an x8 card, going with a SAS HBA is probably a better bet.

From what I've heard, some people have had some issues with Marvell chipsets for NAS usage. If you're considering FreeNAS, you should really look at their hardware compatibility list to find out what the best choices are.