What is the protocol for a surprise birthday party at a restaurant?

I am planning a surprise 65th bd party for my friend at a local eatery, with about 10 guests. Here is the dilemma: I can't afford to buy dinner and drinks for everyone so how do I convey this to the guests? Tell them when I call with the invitation? ' Oh by the way, come to party I am planning but you'll have to buy your own dinner'. I don't want them to bring gifts, just a card. Should I at least spring for some appetizers, but how do I say the appetizers are on me, but that's all, folks. I am a little shy in social situations and have never done anything like this before, but this guy means a lot to me and I want to do it right for him, but at the same time not max out my credit card. Having it in someone's home is not really an option, as his friends are spread out over a wide area and this is one of our favorite restaurants.Any ideas? Thanks!