Our clients get between $200 and $2,000 on average. One guy got a huge $15,000 return, but thats cos he had a lot of business. It varies really. Even though i work as a tax accountant, i do my own taxes - will be using e-tax this year.
Some clients have the easiest tax returns, yet bring it to us to do it - if I was running the business, Id charge them $50 for the 10 min job instead of $140. Judging by your previous tax returns, you can estimate how much you will get back, if its going to be a lot, then might as well pay for an accountant to take care of it.