Which gaming headset is best for budget?

Sennheiser ear buds + a condensor lavalier mic. It's what I use. The Senheisers will give you better sound quality than any gaming headset you try, and a condensor mic will pick up anything in the room. Just adjust the sensitivity/transmission level in TeamSpeak/Mumble and you've the perfect setup.

Sennheiser CX270 and a lavalier mic will cost you less than $50 off eBay. You don't even have to wear the mic. I leave mine sitting under my monitor.

See my siggy for details