Rflong if you do get any negative price tag buildings - you can fix them by saving the building to your library from the game, then bulldoze the one in the game, then place it back in the game from the one you moved to the library.
I have found out if buildings get that negative price tag it causes weird lags and freezes in a world - but by doing that to every building that has a negative, seems to fix it.
I kept coming up with that problem while testing Gems world, that some apts would have a negative price on them - in particular unfurnished apts - which was part of the her lag problem. Once we got rid of all the negative prices the last of any lag she had went away. This was the most effective way to fix the negative prices.
It is an EA glitch that began with Ambitions and the City Hall celebration call. How it went from that to glitching prices i have no clue - but the same fix we had for the town hall fixes the prices. Odd, but it works.