I don't think you're going to find much for $50. You're probably better putting something together yourself. Those cheap kits tend to just have junk in them, bandaids, tweazers, maybe a piece of gauze if you're lucky.
I got a pretty decent one from Costco for about $100. Has lots of gauze, slings, sterile pads, medical sizors, sting and burn treatments, etc. I carry it around always, and have even used it a few times to patch up other people in the real world. Once cut his hand badly on broken glass, the other I think he stabbed himself in the hand with a knife trying to work on his motorcycle. Insisted on doing the ride anyway... That one required much gauze, and duct tape, no kidding.
Oh yeah, and make sure you have several pairs of gloves, and ALWAYS use them when working on strangers.