Go out to a local cocktail restaurant where you like the live music they have performing and offer to buy 4 hours worth at your home. It will be about $500 or so, get something instrumental like a guitarist/bassist duo, marimba/ conga duo, piano/ string bass, organ/ guitar duo. I would skip the stage-style acts (singers/ DJs/ dancers) because you will most likely miss your target audience. Just settle for a sedate, tasteful background set.