it costs about £15 for 4 sheets of depron, add another £20 - £30 for ancilleries like rods etc, rob some of the gear from your other planes, and you off.
i bought a P51 as my intorduction as it was cheap, and what a mistake i made.... i build the blu baby as my first scratch built and my god, what a success
if i bought the P51 now, i know i could fly it. if you do need to buy another plane, may i recommend the super cub, it is a well proven play ground for all skill levels.
either that, or go through what you have, and pick the slowest, most high winged plane you have. repairs to foam can always be achieved with some hot glue (dabbed in places) or gorrila glue (you need to pin/clamp in place while it sets) and you will have a fix line stronger than the origional foam itself