I have a 2009 mini with 1GB RAM. It runs as well as my 2006 Core2Duo MacBook, which has 2GB RAm.
Unless you have a buttload of programs open (iphoto, imovie, itunes, handbrake etc.) then 1GB will probably do for now.
It's much cheaper to upgrade the RAM yourself, but it's not for the squeamish. I'm going to upgrade mine to 4GB once the mini's not to shiny and new. But that's only because I'm greedy, and do a lot of video and graphics work. And run games 🙂