I just used epoxy (sparingly )on my e-flight ultimate. It said to use foam safe CA but the store I bought it form didint sell it (as far as I know) and its like you said, the stuff is so expensive in the first place.

If you use epoxy use it sparingly (as with hot glue and other weight adding glues). Use just enough, dont just glob it all around hoping itll make your plane invincable.

Ive read you can use this "gorrilla glue" on foamies as well, Home Depot is suposed to sell it.