Just write a short, cute note that you're hoping to keep things small and intimate and thus it's ladies (or whoever gets the invite) only. I dictated that some of my wedding guests wouldn't get +1's. People know me, and know that I would be uncomfortable if they brought a stranger to my wedding, so I've gotten absolutely no pushback on it. Right now it looks like we'll have 60 people at mine, and that's a great number.
I also bought my dress before I got a ring.

But it was SO CHEAP it didn't require a deposit. And we'd been talking about it for a while. Alf didn't get scared when he saw the giant white garment bag in the closet.
I'm usually really open-minded about such things, but asking people to put money toward your wedding by throwing a party is just tacky. That's about it.

If you can't afford a "typical" wedding, get married at City Hall then have a potluck where you celebrate with friends. You aren't owed a fairytale wedding if you can't afford one.
And once they're married and struggling to make ends meet, they'll be wondering why the heck they spent so much on the wedding instead of taking that money and using it for their actual needs.
My own wedding's just over a month away and I'm saying goodbye to my money about now.

I'm actually stressing more about my class projects than about the wedding so....I think that's a good thing?