iphone 3gs or what may be a better deal?

[*♥*Roxyrock*♥*]

so im looking into buying an iphone 3gs (because im on a tight budget) i dont have money to just throw around on a phone! but i def want a smart phone for many reasons as in instagram to keep up with family!!! but as i said before i want something on the cheap side! so my question how much can i get an iphone 3gs ( not up for upgrade yet) for as in if i walk into my local at&t store whats going to be my price? or is there a similar phone that i can still get instagram on for a better price! thanks good people of yahoo answers! :-)