One of the more desired SYS4/6 games. Hard to find one without playfield wear or backglass delamination or crazing.
If the game has been in storage for 15 years, then it may not fire up at all. If the battery has leaked onto the MPU board then it can be a time consuming excersize. You can buy replacement boards.
If it is your "Holy Grail" pinball, then you might pay up to $1200 for this title as you describe it.
A fully restored Gorgar can fetch $1900 - $2300.
Dealers would ask for stupid prices around the $2500 - $2800 figure, which is way too much. The work they do would be the bare minimum to have it presentable and working.