I've just returned from the Columbus, GA gun show where I picked up a P6 with two factory mags, mag case, like new black leather holster, box, manual and a test target. Considering what I paid for the Walther PP in .32ACP that I traded, I estimate I have $425 invested. Mine was made in April of 1979. It's in VG condition outside and shows almost no use inside. I had my choice of two.
J&G is the only place that I see them available although there may be other sources. J&G wants $370 with one mag and the box. No holster, no mag case etc. BUT, they'll sell you a mag holder for $7 and a factory mag for another $40. Add $22 shipping and the transfer fee and the price goes over $450.... and you don't get to inspect it until it arrives. It's obvious that J&G strips the extra mags, mag cases and holsters (if it came with a holster) and sells them separately. I don't like companies that do that, especially when they price high anyway.
The supply of P6 SIGs seems to be drying up and I only see the prices going up like most surplus guns do when no more are available from distributors. If you got one early at $250 - $350, be pleased. IMO, what I paid is pretty much the going price now.