How to do an affordable open bar and catering?

Well, if you went with a morning/afternoon wedding, brunch catering is 50%-75% the price of dinner catering and then you could cut down tremendously on the alcohol with just mimosas and Bloody Mary's. If you're set on dinner, then do BBQ catering with just beer and wine as options.

I agree that alcohol is a place where you can make cuts, especially for a daytime wedding. You can also ask about doing a consumption bar.

You can do a beer, wine signature drink bar
BBQ Italian food is cheaper see if you can find a restaurant to cater

Buffet is usually cheaper than a sit down meal, and like everyone else said, a limited bar is definitely an easy way to save money. We are doing an extremely limited bar (2 beers, 2 wines, 2 hours of the reception, signature mocktail) and it is an extra $7 per person on top of the catering and venue costs. It all depends on what you want.