I have Du-Bro .40 size skiis on my RCM 40 trainer. The work very well & coat about $10 for the nose and $20 for the two main.

I just dropped $100 for a Contender kit, another $220 for the engine, and $300 for the receiver, servos, tank, spinner, wheels, and assorted extras and peripherals I needed to construct it. I figure a pre-existing $200 for cutting tools, glues, clamps, pins, sandpaper, razor plane, drill bits, taps, etc. I'll need another $30 to cover it.

But then I'm a nut.

You could do it with a pen knife and a clothes iron for a lot less.

Three things I have found to be worth the cost are: a Great Planes Easy-Touch 22" sanding block ($5.99 ea, I got two and keep 80 and 220 grit on them), a Great Planes T-pin pusher/puller ($2.49), and House of Balsa Alignment jigs (I got two for $2.30).