Hey, let me know something... do you buy the pieces by separate? by generic sets (like 50 of this piece, 20 of that one)? or you take them from ordinay Lego sets releases such as trucks, spaceships and stuff like that?
Your best bet is bricklink.com, and I usually don't buy the specific parts I need for a frame, but just go for useful pieces that o can get in larger quantities for a good price.