You can write $100.

I had a friend register her Volvo based on what she actually paid for the lease (she got a good deal). The DMV told her according to them the car was worth more and they wanted to charge her more. I think she yelled at them and they backed off.

If they say anything, kindly remind them that they are NOT in the car dealer business and should stick to what they can barely manage as is. In other words, tell them to shove it and give you your plates based on what you paid.