If memory serves me correctly, a TZ prototype with red boards was for sale in Georgia or thereabouts in 2002. The game's cabinet was autographed by Pat Lawlor, John Youssi (and perhaps Ted Estes, Larry DeMar and/or others). The asking price was in the $5K range. The game's overall cosmetic condition was somewhat below average.

I recall passing and opting instead to buy a local sample TZ, which was in very nice shape. This sample had the factory-drilled 3rd magnet hole, as expected, and most (or all?) of the prototype features, sans red-colored boards and ramp signs. I was able to later buy the 2 original prototype ramp signs and I installed the 3rd magnet in the factory-drilled hole and added a couple thousand dollars in reversible mods, e.g. fancy etched illuminated apron, working slot machine, Element One rocket, etched lampshade, Invisiglass. . .lots of costly mods.

As I recall, the cabinet art on the protos and samples versus production games was slightly different on the head. Of course, the art on the upper playfield lacked the "flip here" prompt and the main playfield art also had a few color variations. My sample was made in March 1993. As a pricing point of reference, in about 2014, I traded that heavily-modded sample TZ for about $14K in trade value to another experienced collector. I recognize that true protos are valued differently than samples. Nevertheless, this transaction may be a valuation barometer to some limited extent.