selling web template design price

I have a front page web template design. And they like it and ask me if I want to sell the PSD project. I’m not sure how much I should sell it? Also, they like to send me a list of modifications. Maybe they like to add or change something too. I would like to sell the design, but she is asking what would be the price of making improvements? I have no idea about the price. I’m afraid if I set it too high or too low. Does that mean there is another price for selling the web design template? AND another price for making improvements? OR Should I add them together?