It really depends on how much up front work you want to do.
You would want to think building it yourself is cheaper but it isn't,
You can get a Tower Hobbies trainer ready to fly for $280, that includes everything for the plane, radio, servos engine ect..
http://www3.towerhobbies.com/cgi-bin...I=LXCXF4**&P=0
You would still need field equipment, ie.. fuel, glow ignitor, fuel pump (manual or electric) starter (stick for hand starting or electric) and a 12v battery if you use the electric fuel pump and starter, and misc. tubing ect... or you can just buy a field box with all that stuff like I did.
http://www3.towerhobbies.com/cgi-bin...&I=LXL419&P=ML