Fees and taxes are different for every country and market, so this is a very good idea and it would be very helpful for the newbie traders,but you have to put lots of work and gather lots of information about market fees and costs.Most of the traders and holders don`t pay taxes for their btc.Only exchange platforms pay taxes,so you should calculate only transaction fees.
What do you mean by "price of returning bitcoin"?I don`t understand this term.
I`ve been trading with bitcoins for about 3 years and i never care about the fees.
Good luck with your idea,OP.