Well I traded 1 gold key for them, back when gold keys were attainable. I'd say they're worth around 5,000 credits, maybe a tad more. They're not in huge demand. It really depends on how bad you want them as to whether or not its a good idea to trade away so much. I'd never make a deal like the one you got offered... I think this person supremely overpriced them.
However, I traded about 5 full party hat sets for male Herbie outfit... I feel I overpaid... but I didn't care. I just wanted it badly and I'm happy I made the deal.