How much is a thunder five 410 pistol worth?

As with any firearm it depends on condition, options/extras and demand.

Demand is not very high ever since the Taurus Judge. But, it could jump now that they are no longer made.

I would not pay more than $500 for a new one and even then I'd only pay that if it was one with both cylinders.

Don't plan on finding one for less than $380-$420 in good to Excellent used condition.

Since used is the most likely scenario, I'd say be willing to go as high as $450 if in good shape and with both cylinders or some other extra(s).