If you've got a radio to control it, FMS is one good way to go cheap. Actually, you can use the keyboard, but that's not going to help you fly an airplane later on. FMS is free, and if you dig around in this forum you'll find Serial Port > Radio interface plans that work with XP. That's as cheap as I can think of.

G2 is really nice, but (and I may be wrong!), it comes with it's own non-radio controller so you can't fly using the same sticks you will be using with your plane. It's landings are a lot more realistic than FMS. But it costs $200...ouch!

The guy at the LHS almost sold me Realflight G2 when I bought my trainer and didn't know anything. I'm very happy I didn't get it. FMS taught me how to steer coming back at myself, the basics of landing, turning, and such. I get to use either of my radios with it, and can be had with 700 planes and landscapes and a usb interface for about $50 I wonder how much 700 planes would cost you for G2 with their little expensive add-on packs? - Joe

P.S. Is FMS the only Sim you can fly Mary Poppins with her umbrella, and go really slow over yourself to see up her dress?