Our daughter got married August '09 at an "event center" where we had the wedding in the round, then transformed the space with tables for the reception with about 130 guests. The fees were segregated for the event space and bar bill, with catering arranged by us separately. We had an open bar - beer on tap, red & white wine, and the normal liquors (scotch, bourbon, vodka and rum as I recall) and we paid by volume, starting with full bottles and the bartenders eyeballing the partials at the end of the evening and prorating the bottle price. We had advised an ending time on the invitations, which was necessary with the rented space, but is a good idea, anyway (Reception, 3-10pm, for example). As I recall our bar tab was around $1200, and event manager made it clear that that did not include gratuity, which was normally expected to be 15% unless there was some problem that had been pointed out at the time and not addressed to satisfaction. I think I paid them around $1400, so it worked out to around $10.50 a person.

Like Don says, there are some reasons to hire experienced bartenders as they can watch for problem drinkers if you have any. This is probably not as much of an issue with only beer and wine, as I would say the issue of overpouring and wasting product is more of an issue with hard liquor. That said, the experienced bartender can still help keep things in control, and while you can't dodge the ultimate responsibility they do provide a layer of defensive argument in case of a problem - you trusted the professional to turn off the tap when necessary.

Best wishes for your wedding planning. It will be a night to remember for your family and friends.