When you say "Model 10" . . don't disregard the older M & Ps which preceded the model numbers. They are out there and you just have to be diligent in your search.
A couple of years ago, I picked up a 5" M & P made in 1952. I had wanted a 4" but I was able to buy the M & P and a Combat Masterpiece together at the time and I had about a total of $550 in the two.
The 5" M & P is one of my best shooting and most favored 38s and while I'd still like a 4" M & P/Model 10, if I run across one it's fine and if not, that's fine as well as I just love the 5".
If I remember correctly, the M & P was priced at $225 or so - it's been a couple of years. Recently, I went to the same LGS where I bought it as they listed a Model 10 in "good" condition @ $350 and someone had already snatched it up.
Two years ago, I wavered on a 4" Model 10 dash something at a store in Tucson, AZ that was in mint condition - never fired. They ahd $350 on it and at the time, I felt it was overpriced. I've regretted it ever since and if I ahd the opportunity over again, I'd snatch it up in a heartbeat.
As mentioned - geographical area has an affect on the pricing as well. The one thing I've been noticing though in my area is that the prices keep working their way up.
Of you find a good one - it's worth whatever it's worth to you. If I remember correctly, a new Smith Model 10 is around $700 or so . . . . a used vintage Model 10 at say $350 may seem high to some . . . but if you want one bad enough . . . the vintage at maybe what some consider a "higher price" of $350 (as an example) is going to shoot just as well at half the price of a new one.
Good luck in your search!