For a dealer I would say that's a buy price offer less OTD and see what happens , Here in the Toledo area you just don't see many of the 5906 and when you do there 450 plus in price.Stopped by a store in the middle of nowhere and they had a 5906 with 1 mag and round guard. Asking $399 before tax/Background check. So OTD it would be around $440.
Whats a good price? It is in 90% condition. No box, or papers.