Critterhunter,
As far as cost goes there is no way a plane in the 10 lb. class can be electric powered anywhere near the cost of IC power.
With a good 26cc. electronic ignition engine going for around 275 bucks it's no contest. Yes electric can be awesome in giant scale and some precision pilots prefer the control it gives them, Dave Patrick comes to mind, but I think he has deeper pockets than many of us.
Gasoline power is definitely growing due primarily to the low cost of regular gas (can't believe I just said 3 dollar a gallon is cheap) and the improvements in electronic ignition systems making them more user friendly, as the timing is automatically retarded for starting, the guy's I fly with that run them just use a leather glove, no electric starter needed.
Building with foam, well most of the better ARFs are balsa/lite ply these days, but foam does make good core material for sheeted wings.
Pete