[AccessD] Maintenance Fees?

Hello,

I have recently written an app in MS Access 2010.
Application went pretty easy, however I am getting calls about "tweaking"
the application or making enhancements. So I was discussing with them maybe
a maintenance fee?

Does anyone charge past clients a monthly maintenance fee? or is it a
straight bill rate time number of hours you work on "whatever"?
If you do, can you give me a ball park range for the east coast of the US
of A.
PA to be exact...

any help would be appreciated, thanks!
-- 
John Serrano