You should be happy that you've managed to sell 100 tickets to an upcoming show you have (though don't necessarily expect 100 people to turn up). You should also be happy that there's a lot of promotion around the gig, and that there are a number of people making an active attempt at getting people along to the gig. You sound like you appreciate both of these things, and that's great.
What you shouldn't be happy about, which has already been mentioned, is that you effectively just did $1500 worth of work for the promoters, just to play this gig AT ALL. Granted, you aren't paying anything to play, but that's only because you were able to sell 100 tickets. If you couldn't do that you'd need to pay, so your gratitude is effectively determined by your indepenent ability to pull a crowd. If you can do that, why the heck are you hooking up with a bunch of guys who force you to do unncessary marketing work?
The pay-to-play schemes are a scam regardless of whether or not you can comply with their demands. If you can't pull the "required" crowd, you have to pay money to play to that small crowd. In your case, that would've been $750 you'd pay to play to 50 people (for example), that you apparently could have pulled without their "promotion". I'll repeat that: You play to 50 people, you pay $750, and the "promoters" do nothing to help you get that crowd. I wouldn't be happy about that if it were me.
The "prestige" of the venues, bands, and promoters associated with these schemes is all bullcrap, used to trick people unto risking their own finances just to play a gig. The "prestige" isn't pulling your crowd, not really. That's why you're selling tickets, and not them. The "prestige" also isn't writing your material, rehearsing your band, or organising anything else that's getting you guys together on the night. You can either build your musical career on your own respect or someone elses, but the respect of others will never really earn you anything, no matter how close you are to it.