Open Question: What was the purchase price of my home?

I bought a home with a purchase price of $111k, BUT $8k of that was paid for by the government as a rebate/tax credit (first time home buyer) and another $4k was personal property included in the terms of my offer. The net purchase price was $100k. My property tax assessment came in at $113.6k. What case law (or other evidence) can I use to prove that the purchase price of my house is net of the rebate from the IRS? Isn't there some sort of case law regarding rebates or tax credits. The house is in the state of Wisconsin.