OP, if money is tight for you at the moment and you can't afford to help fix, then tough luck for your buddy - he invited you to play on it. If he's wealthy and doesn't care, then even better.
If you want to pitch in because you can or because you want to, then there are cost effective solutions to get the speaker replaced. You may be able to get a decent new MCM Audio or more pro grade used 10" woofer in the $35-90 range as a replacement. No service tech needed, just get the amp model, total watts, and individual as well as total speaker ohms specifications. Whatever recommendations you get, run it by Fender to make triple sure, and wire the replacement speaker back up exactly like the damaged one. Take pics of the original speaker wiring before you disconnect for reference when you replace.
If you are inclined to help out, set a budget for what you can contribute, propose that to your buddy and let him take it or leave it.