That really depends on a number of factors,
Condition. The cleaner and less used one appears, the more it's worth.
Stainless or Carbon? Stainless are worth more, but I'm not sure how much more. I've seen them for $500.00 or more, but personally that's a bit high.
LGS or private seller?
The last one I bought, right after the first of the year, I paid $349.00 plus tax. Gun, box, paperwork, two magazines. The same shop sold one about a month previous for the same price. I never saw that one, but as I recall, the listing was similar.
I consider that a bargain price, but $450.00 for a non stainless version is at the top of what I'd pay.
That's just me and other people might just say I'm cheap.
Also, figure into your price calculations the cost of a new recoil spring. Factory ones are sometimes rare, but Springco makes a very nice set that will be yours for around $20.00, including shipping. Even if a gun is listed "ANIB" I replace the recoil spring. As S&W does not have any replacement 3rd Gen frames, it's cheap insurance.