your best bet is doing the b2g1 free right now at ebgames/gamestop on used games/accessories/dvds. The gba player is $30 before discounts, but if you buy that, and a couple of used games(something like castlevania ds and super princess peach) you would be getting all 3 for $60, or $54 after the more card(additional 10% off) which puts the price at about $18 each.
that is my best suggestion.
Or you could simply wait a few months, i have a hunch once the WII comes out, then ALL of the gamecube accessories will get a decent price drop