Hi K. -
Congratulations on approaching your son's 1st birthday...how exciting! :)
During my son's party (we had it in Hawaii where first b-days are a HUGE deal), most of his guests were also adults. We had a few kids, but they were mostly pre-teens.
What we did was organize a party through Dave and Buster's...not sure if there's one in your area, but something along those lines like Gameworks in Channelside could be another option.
For the menu, we chose something really tasty yet nominal in price - a pasta bar and free refills on tea and soda - and each guest was given a $5 reloadable game card that he/she could use at the arcade. We brought our own sheet cake from Costco. For doorprizes, we purchased some logo items from the gift store, and for the biggest prize, we purchased a gift certificate for two to attend the restaurant's Mystery Dinner Theatre (at the time, I think the value was like $50). The door prizes were awarded to various winners of a multi-level quiz show type game based on fun facts about Isaac. Each guest was given a fact sheet that they had to read and then put away before participating in the game. They all really got into it.
Even though we had about sixty guests, we had SO much food left over from the party that we ended up going across the street to Ala Moana Park, Oahu's version of Central Park, and gave the extra food to the homeless.
All in all, we had a great time and because Isaac was so young, he didn't miss having his favorite theme characters present. The adults had a great time and actually stuck around until the very end...of course, we made sure to play up the coming game and doorprizes so that they'd have an even greater incentive to stay. ;)
All in all, I think we spent about $1000, but that was a very reasonable price considering that most first birthday parties in Hawaii average around $2k - $5k!
Plus, Isaac made about half of that back with the generous gifts he received.
Have a great time! Blessings to you and yours.