Sad news hope you get sorted buddy, Try sticking the reg in auto trader see what they say it’s worth , I’d think the mods possibly bring the value down as a lot of people looking for a low mileage gti would want it to be completely standard.
Stick some more info/pics up
dsg or manual
Service history /cambelt history
Colour
What spec Lights ,Seats ,clocks
Ect ect