You are going to be very hard pressed to find a Mountie or 1897 that is a decent shooter for less than $500. You'll probably spend around $600 or so for a Mountie. IMO, they are worth the money, being one of, if not the best, 22 lever ever built.
A less expensive alternative is available from Henry. I have the Henry Frontier, Model H001T, which has a straight stock and an octagon barrel. It's awful close to a Marlin 1897 in appearance, and it was $339 new. The action is smooth, and it's shoots extremely well. It's not a Marlin, and although well built for the money, it won't last like a Marlin, but it's a great little shooter, especially for a kid starting out. They do make one also that you can get for around $250, the H001, but it has a round barrel and plastic parts, like the front barrel band and sight assembly if you really want to save.
Hope that helps!