Cost to build a playhouse?

Question:My husband and I want to build a 5 ftx5ft (or something similar) playhouse for our kids. Using the cheapest building materials available, with no fancy flooring, or inside walls (we'll probably leave the 2x4's exposed inside, and cover the inside with some sort of weatherproof wallpaper/covering..not sure yet) How much do you think it would cost? I was thinking with the wood for the frame, outside walls, roof, and misc. wood for the door,shutters and a little table for inside, would be all we would need. My husband and his dad, build a 20ft. workshop last year, so the labor part, we have covered, we just dont know how much the material would cost. Nothing fancy. Ballpark??

Answers:
Your looking at under $500 easy.