That sucks bro.
You know that same shit happened to me when i first started doing installs. rush rush rush...then in the end no money. I am embarrassed to say this but the guy that rushed me and decided he wasn't gonna pay me....ended up loosing his system. A week after I installed it, I removed it for him. That was about 12 years ago, I was young and dumb.
Only advice I can give you is if your friends want you to install anything for them, make sure they provide everything except maybe the tools. If you have to use your materials, make them pay for it. And most importantly, if they are not going to pay you for your time...make them help.