Well, if that had any basis whatsoever on the price of a car I could go get a Ferrari 250 GTO for $5. lol
In the case of a modded car or a unique car the price often goes up (due to the mods and work/maintenance done) but the market of people interested shrinks.
Best thing to do is look at what the base, normal car is going for in your area to start. NADA for the car is $7750 without knowing all the options. Now, for someone looking for a modded car you have already done a big jump with the K04, looks like it's lowered as well. A good rough guide is add around 50% of the cost of the parts (no labor) depending on how long ago it was done. So depending on what else you have done and options on the car, you're probably looking around in the $9k region.
Ultimately a car (or anything) is worth what someone is willing to pay for it. So figure out what you would LIKE for the car, post it for sale and then let the haggling begin.