It all depends on your market. If you are working for an advertising client or in a pre-press environment, here in NY you would charge us$250/hour. If it was a corporate client or internal usage, maybe $50 an hour. If it's a private client, that's a little harder. As Fd-regular says, you can get retouching in India for $2 an hour. I had antiques website I was shooting for who used an Indian retouching house for all the color correction and silos. You couldn't believe how bright and saturated they made these fine old antiques look. It turns out they had no point of reference, so they just punched up all the colors to what seemed to look good to them. ( and then blamed me when the clients complained!)
In my experience, when you have a client and they haven't given you any pricing guidance, the best thing to do is to give them the price you think is fair, meaning that if they accept the price, you will do the work without resenting them. At the same time, tell them that although this is an industry standard price, you are willing to work with them on the budget.
This way, the"budget" is the bad guy if they ask you to do it for less, and you can still be friends.