I've seen two sold for $350 at gun shows in the last year. The first, I was going to ask about/buy, but the dealer had left his table and when I returned, another dealer was buying it. The second, I was with a friend and he spotted it first and negotiated it down.
Marked prices run from $400 - $600 at the shows and stores I go to. I would not pay $500 unless it had box/docs and was in 95%+ condition. However, the price on the old smiths is going up as the vast pool of police trade-ins begin to dry up. In five years, we may be kicking ourselves for not buying more model 19s.