Brand new kits are selling for $5900 (when on sale), there is no way you will get anyone that knows the kit to spend $5000 on a used kit. Well I guess there is one born every minute, but finding them might be tough.
I doubt you will be able to get more then $3000 for a used kit, and that is going to depend on which turbos the kit has, mileage and condition of everything. The last one that sold on here was near the $3000 point.
Here is a link to one where the starting price was $3500.
GLWS