Do people really ask friends to pay for their parties?
Don't get me wrong, if I am invited to a dinner party out on the town I have no problem footing my bill. I'll avoid high priced alcohol and stick to something from the middle range of the menu. When a host informs everyone at the end of the night that they should just split the bill 8 ways and I have to subsidize everyone else's filet mignon and alcohol induced stupor then that is a different beast entirely. Maybe it's just living in a relatively small Midwest town that I don't run into this, or possibly I just don't have the tolerance to put up with anyone who would pull this kind of stunt long enough to get a dinner invite!
If you can't already tell, this is a great way to lose a friendship or a business acquaintance. The last time I checked common courtesy hadn't been taken out back and shot so if you plan to have guests split the bill for dinner, make it straightforward and easy. Ditch the open bar and coordinate with the restaurant to offer a package deal for dinner and 2 drinks. When you send out the invitation be sure to include a line stating, "While I am picking up a portion of the dinner, guests are kindly asked to pay $20 to help cover the fun time that we are all about to enjoy together!". This kind of invitation may turn off a few people who were just looking to score free booze but in the long run your real friends will appreciate your honesty and the good times you all shared!