A Local Church
Check in with churches and community centers in your area for other possible party locales. Often they'll have a gymnasium or multipurpose room that can easily accommodate a birthday celebration, along with a kitchen for any food storage or prep space you might need. Plus, any rental fee is probably going to be far less than what you'd pay to rent a room at a restaurant or banquet hall.
Organizations like this could also offer the opportunity to lend a socially-conscious approach to your party. For example, if the church has ties to a food pantry, one of your activities could be making and decorating cookies. Set aside some for your party-goers, and have them put the rest in snack bags for distribution.