I want to go to dinner for my birthday; some of my friends think the restaurant is expensive. What should I do?

It's your birthday AND it sounds like you're the one planning it. If the guests don't like it, they don't have to come. If you feel like some of your friends may lame-out on you because they think fifteen bucks is too rich for their blood then I like your first option of just buying appetizers yourself for everyone to eat. That puts the bill entirely on your shoulders but guarantees everyone will show. I don't like that you're putting yourself in this position and hope that from now on you'd instead let someone else throw the party for you so you can enjoy your party AND not be handed a bill at the end of the night.