V8P to V12 G1 is a huge step up in terms of stability, but you probably already know that. Just make sure it is the right boat for your intended use and skill level. If it is the wrong boat it doesn't matter how cheap it is, it is a waste of money.
Regarding the value of that model, there are very few people capable of paddling an elite ski in the USA, and V12 G1 is a very old model. As such sellers have to drop the price pretty low to get rid of them. I have owned two V12 G1. I sold the black nose, which was quite heavily used, for $600, and the red nose, which was in decent shape, for $1200. $2500 is a reasonable price for a used second gen V12, but I don't think there are many that would pay that for the first generation ski.
Current Skis: Nelo Vanquish AIR, NK 670 double, NK exrcize, Carbonology Feather, Think Jet, Knysna Sonic X
Former Skis: Epic v10g3, Kai Waa Vega, Epic V12 g2, Epic V12 g1, Epic v10 double, Nelo 550 g2, Fenn Elite S, Custom Kayaks Synergy