Some of the tree removal/pruning companies will deliver wood chip mulch for free if they're doing a job in your area. You may need to put your name on a waiting list. Sometimes there will be some large twigs that need to be picked out ,but other than that I've been happy with the loads I've gotten.

It is wise to know where the debris they are chipping came from (like somewhere in your neighborhood, where you can see what's going into the chipper). I have found plenty of poison ivy in the free mulch I've received.