Don't know if this is what you had in mind, (and it probably won't be of much help unless you can find it on some abandonware site), but in about 1989-1990 I used a very nifty program called Buy Your Home (IIRC). I'm not a programmer, but at the time I recall thinking it was probably just a fairly simple GUI shell for a spreadsheet engine. (Cost was about $20 US at the time, IIRC.)
It was primarily intended to allow comparing
renting vs buying, but was easily adapted to compare buying this house or that house, etc. It allowed you to enter assumptions about your projected annual income and expenses, income increases, rent amount, home selling price, mortgage amount and payments, interest rate, taxes and deductions (pertaining to buying vs renting), projected appreciation (or not), how long you expected to stay in the place (renting often financially better than buying if only staying a few years), etc., etc. IIRC, it also must have had some basic tax estimating functionality built in, based on existing U.S. Federal tax regs at the time.
The way it was set up, you could also use it to compare different projected income and/or mortgage amounts for the same home purchase, e.g.:
• projected income if spouse works or not
• paying only the required mortgage payments vs paying more than required each month
• interest only w balloon vs fixed or ARM
• minimal downpayment with higher mortgage vs larger downpayment & lower mortgage
• different loan terms (e.g., 15-year fixed vs 30-year fixed)
• investing more available funds in a more expensive home vs a less expensive home with the difference in funds invested elsewhere
• how much difference it would make over x years to buy down a loan half a point when setting up the mortgage
• etc., etc.
I'm pretty sure I still have the program on a 5.25" floppy (which might have deteriorated beyond use by now) somewhere in my storage unit (hour and a half round trip and a couple hours of searching), and probably on an old HDD somewhere in storage, but my current circumstances don't allow me to go look for it.
I didn't find it online just now in a quick Google search, but if it is no longer being marketed, you might find it on some of the abandonware sites. if you can't locate it anywhere, you might be able to find or create a spreadsheet template that would allow you to plug in various scenarios along the lines of those I've mentioned or whatever might better fit your circumstances and needs. Seems like asking in some of the Office/Excel forums might be a good place to find a template that could be readily adapted to your needs. ...(Unless Perry Mowbray above is volunteering to write one
)
Good luck!
