How much would it cost to get a new phone before my upgrade?

I have a iPhone 3G from AT&T & I got it as an early birthday present in February 2010. I accidently dropped it outside my local McDonalds after school one day & it hasn't worked since. I refuse to not have a phone for 6 months during my freshman year. So I wanna know how much a replacement phone I guess , cost before my upgrade? Without a 2 yr contract. Like a phone I can use for 6 months up until I'm eligible for an upgrade.