I had over 100 people at my wedding and I would say 75% were heavy drinkers. Our wedding was also at night at ADH (we like to party, what can I say?). My wedding was over a year ago but I believe we paid about $28.00++ for alcohol. This was the lowest of the open bars.
It basically had all the basics - vodka, rum, tequila, gin, beer & wine.. and none were generic brands. Just the lower end. So basically they had Smirnoff vodka as opposed to Grey Goose. Cuervo instead of patron. In my opinion, you're getting free drinks, no one's going to care that it wasn't Grey Goose
Anyway, if your guests are anything like mine.. there was no way we could've done a BOC. No way! I personally had at least 8 - 12 drinks... at $8.00 - $12.00 a pop.. yeah, no way.
As for money, you can have your open bar count toward your f&b minimum. Since my wedding was so late at night, I didn't mind having the fanciest food in the world. So, it evened out with my liquor cost. I had to spend $100 a head... and did so perfectly. My menu had pastas and steak.. but it was a buffet. No added extras - but people had plenty to drink.
So, estimate how much drinking your guests will do. I think it depends on the atmosphere of your wedding. Mine was not a typical wedding reception - I literally had a party so there was no option when it came to open bar.