Adding a function

Hi
Asked the Hikashop team about a function in the shop that I would really like to have but the response was that there is not enough users that's asking for the same thing so they feel no need to make this. I totally understand this but they also sugested that I could see if anyone was interested to make one plugin or function for me so here goes.

"All prices that I get from my suppliers are prices without tax. All prices that I set in the shop are prices with tax AND some margin for me.
Setting the price on a product I can choose to set the price that I want in the shop and it then shows me the price without tax. The problem is that I have no way of knowing the price that I pay for it myself and it's a royal pain to update all prices manually if something changes.

My question is this. Would it be possible to add a "margin" function that I could set on a category or per product so that I would have the IN price and the OUT price displayed in the backend instead of just the OUT price?

Example:
Say that I have two categories, red stones and blue stones.
The red stones are unpopular and I can't have more than 15% margin on the "in" price on them but the blue ones are very popular and are possible to sell with a margin of 40%.
If I then could set these margins on the categories it would be really simple to adjust the prices if I had to, even if there would be hundreds of products each."

I hope that was understandable and my question is now, is there anyone with programming knowledge and time on their hands that would be willing to make this for me and how much would you like to charge me for it?