The best Model 97 I've bought was also the cheapest. It was made in 1954 and had less than a case of shells through it. It had spent a lot of years in a saddle scabbard, but hadn't been shot much. The seller felt bad about asking $150.00 for it, but I didn't haggle with him. This was just last year.
The most I've paid was $450 for a Black Diamond Trap Model 97, in pretty good used condition. Of the seven Model 97's I've got right now, that was the highest priced one. Most were in the $300 to $400 range for good solid guns.
My wife shoots one that was made in 1899, which is a solid frame gun. Her backup gun is also a solid frame gun, but has been refinished and is very sound. I paid $400 for that gun, but it was in with 6 other firearms that I bought at the same time in a package deal.
Check out the gun and make sure the frame isn't cracked where the barrel fits into it. Also check the lugs on the end of the action bar, as those get worn. Another area to check is the inside of the magazine tube and make sure it doesn't have severe rust in there, along with a broken follower spring. Also, check to see if it's been rechambered for modern 2 3/4" shells with star crimps, and isn't still chambered for 2 5/8" shells with roll crimps.
If it's a take down gun, make sure the fit between the frame and barrel assembly is tight. There should be no play between the two pieces. There is an adjustment cog on the inside for taking up any slack. You'll want to make sure there is still some adjustment left on the cog.
It's been my experience that take down guns go for more than solid frame guns, though women usually prefer the solid frame, since the reach to the forearm is about an inch shorter.
For me, it would have to be an exceptional gun, that I really wanted, before I would pay $800.00 for it. I've found that patience, and letting the word out that you're interested in that model will bring them to you for a reasonable price.
Hope this helps.
Fred