SL8 to a G 36 Value?

Quite a while ago my Wife got me an H&K SL8. Kinda neat but didn't really care for it. Then she found a place where they transformed my blue rifle into a black, folding stock G 36 wanna be. It got a bolt with a twin extractor and it was cut and threaded. Now retired and an upcoming gun show I think I'd like to sell it. I really have no idea what to price it. I'm pretty sure that the poor gun never held a price well and the re-cost more than the gun. Ideas where to start? Last, it's had less than 100 rounds down it. Shame.

Thank you Sir. It's off to the show now. I'll see how it goes. Show goes on tomorrow. YouTube has a post of $3,500 - $4,000