The cheap or free oil changes aren't worth it, I think. I can do an oil change on any of our cars in 20 minutes in the driveway, and that's taking time to drink a beer while doing it. The trick is to get a good floor jack and jackstands and a creeper, and also to buy oil and filters in advance, when you are already driving by the auto parts store. I also check the paper for sales on motor oil and stock up when it goes on sale - so far I have not paid more than a dollar for a quart of oil.
It would take me more time to drive to the oil change place, wait for them to do it, then drive home. And the times that I have available to drive to an oil change place - such as Saturday afternoon - are the times that everyone else has available and want it done also, so there is always a line.
Ted