Reddit mentions of Scotch Brand Interlocking Fasteners, 2 Sets, Clear

http://www.amazon.com/Scotch-All-Weather-Fasteners-Inches-RFD7090/dp/B00347A8EO/ref=sr_1_7?ie=UTF8&qid=1419056661&sr=8-7&keywords=3m+dual+lock

Sticks to glass, and pretty much anything else. Removes without any residue.

Unless you're going to be doing a lot of them, I'm going to just recommend something like these

Try some 3M dual lock pads like they use on the back of the EZpass transponders and such. I use these on my cam and it's very easy to take off and put back up. https://www.amazon.com/Scotch-All-Weather-Fasteners-Inches-RFD7090/dp/B00347A8EO/

Here are a few things I just bought for our my board:

Scotch(R) All-Weather Fasteners, 2 Sets of 1 Inch x 3 Inches, Strips
http://www.amazon.com/gp/product/B00347A8EO?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00

Portable External Battery Charger Pack
http://www.amazon.com/gp/product/B00QRW8R8M?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00

Goal Zero 14101 Luna USB LED Stick Light
http://www.amazon.com/gp/product/B0045XRK06?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00

Fender Mini Electric Guitar Stand
http://www.amazon.com/gp/product/B0002DV7U2?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00

To be honest, you're asking a lot for your budget. If you want to sit next to the speaker and be able to listen to it at a reasonable volume, something like this would probably work well enough: http://www.amazon.com/Portable-Wireless-Bluetooth-Speaker-High-Def/dp/B00GZC35YK/ref=sr_1_9?s=electronics&ie=UTF8&qid=1427349938&sr=1-9&keywords=portable+speaker

But if you want to be able to actually be active and hear your music, you're going to have to get something much bigger. That said, you can do it without breaking your budget.

My advice would be to by a pair of these: http://www.amazon.com/AmazonBasics-Powered-Computer-Speakers-A100/dp/B00GHY5F3K/ref=sr_1_2?ie=UTF8&qid=1427350132&sr=8-2&keywords=usb+speakers

Power them with this: http://www.amazon.com/Battery-13000mAh-Portable-External-Cellphones/dp/B00K64WR9C/ref=sr_1_1?ie=UTF8&qid=1427350210&sr=8-1&keywords=battery+pack

And fasten them all together with this stuff (it's incredibly strong, trust me) http://www.amazon.com/Scotch-All-Weather-Fasteners-Inches-RFD7090/dp/B00347A8EO/ref=sr_1_7?ie=UTF8&qid=1427350273&sr=8-7&keywords=dual+lock

That comes in at around $49 and while it's not going to blast your music, it will do you much better than any sub $50 bluetooth speaker.

Now if you're willing to spend some extra money, get one of these: http://www.amazon.com/Ultimate-Wireless-Bluetooth-Speaker-Speakerphone/dp/B00E9YIFQ4/ref=sr_1_8?ie=UTF8&qid=1427350482&sr=8-8&keywords=ultimate+ears

I can attest from personal experience that it's a pretty powerful little speaker, sounds great, and you can pair two of them for stereo listening.

Maybe try something like this Scotch(R) All-Weather Fasteners, 2 Sets of 1 Inch x 3 Inches, Strips, Clear (RFD7090) https://smile.amazon.com/dp/B00347A8EO/ref=cm_sw_r_other_apa_i_QL7PCb0PW60YH

While the naysayers are right and it's a bit unsafe I recommend strong velcro tape like this, in the case of a crash the battery pack would be ripped off, but under all other conditions that velcro will hold anything securely in place even at speed.

If you decide to go with velcro, use this:

http://www.amazon.com/Scotch-All-Weather-Fasteners-Inches-RFD7090/dp/B00347A8EO/ref=sr_1_7?ie=UTF8&qid=1301578466&sr=8-7

I would use something like this plastic velcro which could also give the games a floating effect from the back. You could alternatively use standard velcro but it would be harder to keep them perfectly level.