Can any tablet run my cacoon JS?
No, the CocoonJS launcher requires Android 2.2 and up. Also your tablet must either have the Google Play store app installed or be capable of installing, and running it. Some Android tablets are not capable of either. Especially the cheaper ones.
I saw some tablets on ebay for like 50-60 bucks, will that be enough as a developer to build, sell, and play games on?
I seriously doubt it. The truth is you get what you pay for, and even if a $50 or $60 tablet could run, build, and play html5 games wrapped in CocoonJS the performance would be very disappointing.
If your looking for a tablet to build, sell, and play on you will probably have to spend at least $200. You should first research all the Android tablets, and ask all the Android developers that have games for sale on the Google Play store what they use and recommend.
If your looking for a deal I wold recommend the 16 GB Nexus 7. It has a NVIDIA(R) Tegra(R) 3 quad-core processor, Android Jelly Bean OS, and Google Chrome is it's default browser all for only $200. I got one as a Christmas present this year, and this thing was built for people like us <img src="smileys/smiley4.gif" border="0" align="middle">