J.R.
Check out local recreation centers. Mesquite, Dallas, and Garland all have rooms available for reservations during regular hours that are less expensive. Most Dallas rec centers also have a kitchen. Good luck with the party!
I almost forgot about Samuell Farm in Mesquite. They have a fairly large building with a kitchen in it that can be rented out for a donation. We had a birthday party and family reunion there before and it worked out great!