I sell a self hosted web app (http://duetapp.com) that generates 3-4k a month. It used to be higher, but I haven't given it the attention it deserves in a couple of months.
Where do you advertise? Is your web page the only selling channel you are using?
I don't do any paid advertising at the moment. I get a decent amount of leads from two other apps that I distribute for free (http://theanchorapp.com, http://getsoloapp.com), google, and word of mouth.