Headphones for monitoring don't need to be top notch. As long as the sound is decent and they are closed (to stop leakage from both sides) it should be fine. If you can go and listen to them first it would be best.
You could look at some ATH-M20 for monitoring. They go around 30$. Never used them though but they have good reviews.
Take into consideration the bassist and drummer. They need to hear some low frequencies, and in this price range, it could be harder to find headphones having some lows, even more precise ones.