The answer in this case here has to be asked with another question.
Specificity is important.
Public, private, or auction?
There are more prototype games that have exchanged hands above $50K than Capcom's Kingpin.
There are "one offs" that have been designed by manufacturers and later sold to collectors for more than $30K.
Most of these results are not reported.
The highest PUBLIC sale of a pinball machine was Kingpin, confirmed.