mortgage calculator software

I would like mortgage calculator software program to do the following: It calculates the P& I payment and creates and amortization schedule....but also there is an input for the amount spent on "closing costs" to get that loan...say $6500 - each user of course would input their own costs - Then from the amortization schedule, the calculator (assuming one was starting the calculation from the inception of the loan) would pull the principal amount from payment #2, #4, #6, #8, etc and total as the amount "Prepaid Principal" along with the interest saved from the interest amount from payment #2, #4, #6, #8...until that total equaled or just exceeded the $6500 plus the amount of "Prepaid Principal"...the amount they entered in as their "Closing Costs" plus the "extra" money they spent in prepay principal for months 2,4,6,8 etc. Also, there would need to be an input for those not running the calculation from the start of the loan ...they may start at month 34...so the calculator would need run all calculation from that input month as well. The assumption of the calculator is always they will be paying next month's principal this month, so next months interest is saved. The output values that can be saved, viewed and printed are: a full 360 month amortization schedule,if desired, and a report itemizing amount of "pre-paid prinicipal", amount "Interest Saved" and the month number where "Closing Costs & Pre-Paid Principal Recouped" If you can make this calculator, I'll pay you for the exclusive right to the software. I'd like the interface to be pleasant and easy to use, fast operating, and as small an .exe file as possible. Please let me know your costs, and time estimate...if it's doable, that is...