9x the cost of taking it down (if it is a single family & u need to take it down)

Lsywhite
Some additional food for thought (pun intended!). Unpermitted work causes a number of problems:
1. The improvement is not insured. Because there is no official record of the work, if there was a fire, for example, during the re-building, there would be no kitchen covered.
2. If there were mistakes made and say, a fire broke out, because the cause of the fire was sub-standard electrical by the owner, you may have more problems.

3. Lastly, when trying to obtain financing for the property the appraiser legally cannot count un-permitted inprovements, so you might have to lower your price.

If your building is zoned for single family they will likely make you take it out. If the building is zoned for more then single family you might have to bring it up to code.
You can contact the building department and ask questions without identifying yourself. Call and ask them.

The biggest penalty could be that you might have to remove the kitchen. There could be fines as well. Contact your building and safety department and ask.

Yep. You could be forced to abate (remove) the illegal kitchen. Inetestingly, if you have that illegal unit rented out, it is subject to rent control, even though it is not legal.