No fixed amount really. I've got two apartments that I am currently renting out. A lot depends on the person looking at the place. The ideal would be a young professional couple. Expect to pay a premium if you have kids or are a couple of guys sharing the place.
Also when looking at the place and discussing the rent, it really pays to be nice. The bulk of people that show up for a viewing have this strange idea that if you try to be clever and say nasty things, you can beat the owner to a pulp and get a lower rent. That never works. From an owner's perspective, if you are nasty now I can imagine the amount of trouble you are going to be if we sign the agreement. Also after having dealt with a whole bunch of smart aleck I-want-it-all's, meeting someone nice and reasonable comes across as a breath of fresh air.