Congrats on sharing a room, that's a big chunk! The $300 for the suit is the only thing that pops out as crazy, but I agree there isn't much you can do about it. One thought would be to directly ask the store if they mind if you return the suit after the wedding if you aren't happy with owning the suit long term. (I assume you don't need a suit) I think there are unethical ways of doing that, just returning it after the wedding without saying anything would be wrong in my opinion. But when you are getting it fitted there is no harm in simply asking, "I don't mind keeping the suit if it works out for me long term, but if I'm not happy with it during the wedding is it appropriate to return the suit?" If they say no problem, then it's an option. If not, at least you asked.
I'd agree with the others on finding an inexpensive but meaningful gift. We live right next to a potter and often bring his hand made pottery as wedding gifts. We can tell them it's from a neighbor and friend, so there is a connection that means something there to us and hopefully to the couple. It's also very nice pottery, helps a neighbor, and is very functional and beautiful. I like the idea of unique wedding gifts, but that doesn't mean you can always find something both inexpensive and perfect to give. Just don't spend a lot just because you can't find something perfect that isn't expensive.