>How many copy do you think you can sold in the next year?

I don't plan to market it any further, but If someone is interested of course I'll sell it, this particular client is interested in two more copies.

>If a client install this software does that allow you to make some cash on >the maintenance?

Sure, but the maintenance charges might not be enough of a profit to justify a low price.

>Do you charge the support calls of this client?
>
>All of this (and many more) can give you clues on how much you have to >charge for the software.

I charge for additions and improvements, I don't charge for support if it's caused by an omission or error on my part, otherwise I do. Also If he asks for some modification, I would charge only once for the development of that modification, and whatever time is required to implement it in all 3 copies.