Depending on how selective you are about your mulch, you can get mulch delivered to your house for free from a number of tree trimming services, I believe Heartwood is one of them.   

They have to pay to dump the mulch they produce from trimming trees, so to save both them and you money, they will dump a load of mulch at your house for free.  Of course you will have the mulch made from whatever trees they trim that day.  From what I've heard it works out pretty well.   

Otherwise, before I was made aware of that trade, I've always picked up my mulch from mecklenburg recycling which you can get a cubic yard for around $11-12.  Of course you have to pick that up, but if you have access to a trailer or a pick-up, its a pretty good deal and pretty good mulch.