In Canada, you should be able to find a decent specimen for between $250 and $500, depending on condition (field model). If it's a take-down model, there could be some looseness between the receiver and the barrel assembly. In such cases, you want to take it apart and have a look at the threads on the receiver side. It's unlikely that there'd be any damage to those threads, but it never hurts to have a look. The looseness itself is not an issue. The gun could be so loose it's like trying to aim a snake and it can still be brought back nice and tight for about $20 (Assuming that the adjusting sleeve is already at the limit of adjustment. If there's still opportunity to turn the original sleeve, you can fix it for free).
Have a look at the end of the barrel to see if it looks abnormally thin (this would be caused by shooting steel shot through the gun). Check also the end of the butt stock that mates up with the back of the receiver. Cracks in the stock are almost always in that area or on the fore-stock. If the wood up against the receiver is severely blackened, it may be a sign of oil damage to the stock (caused by excessive oiling and storing the gun with the barrel up). If any of these conditions exist, offer the seller a reduced price based on what you can see (except for thin barrels - stay away from those). The other conditions, looseness or oily wood, can easily be fixed (new stock will cost about $100).
Other than those tips, buy one - you'll never regret it. I can help you find any parts you'd need, but it's unlikely you ever will. Maybe a replacement stock or an adjustment sleeve, but if you buy one that needs either of those, it should be obvious and you should get it for more of a discount than it'll cost to fix. If the action cycles smoothly, I wouldn't hesitate to buy any 1897 as long as the price reflects the condition of the wood and the barrel.
What the others have said is all true. Trench guns in good shape are worth around a grand. Riot guns, about $500. 16 guage models are worth about 50% more than the same gun/same condition in 12 ga.
SS