If only, say, 5 of them need to be wireless, you may want to look at the Logitech F710. You can get them "Used - Like New" for $30 with shipping. I can confirm these work extremely well with Linux. They connect via USB, so you don't need to screw with Bluetooth, and the batteries on these seriously last about a year. They're the staple wireless PC controller - very widely supported across the board.

That leaves $150 for 10 more controllers. Well finding $15 wired controllers is surprisingly easily. There are a number of wired Xbox 360-style controllers for that price (but I unfortunately can't comment on how well those work), or you could go with the F710's wired brother, the F310. Again, you can find it refurb or "Like New" for $15 with shipping. If you dig around a bit you might be able to find them for $15 each new. I think I've seen them go that low before. I'm ~95% certain these are just as widely supported as the F710.

The only issue with these is that some people may complain about the fact they have a DualShock layout - ie, both thumbsticks are on the bottom, and the D-pad is on top. Many people like the Xbox style with the thumbstick on top on the left. So it depends what you're using these for. They're great for platformers, less so for racing games and FPS (but still very useable). Note there is a "Mode" button on both that instantly swaps the functionality of the left thumbstick and D-pad, which works very well. But, it doesn't swap their physical positions. :-)

Good luck on your search!