I was gonna suggest the classic Lyman 48 sight for your rifle, but it occurred to me that would only fit bolt action rifles.
Have you tried Marbles? They are still in business, and doing a brisk sales on classic antique-style sights for lever action rifles.
Another alternative is Williams. They offer several for flat-sided receivers like the Winchest and Marlin.
Yes, unfortunately, the collectors craze has bumped up rifle sights to incredible prices.
You don't intend on using a tang-mounted sight, do you?
That is probably no recommended, as the M71 has heavy recoil, and a tang-mounted sight can be an eye hazard.
HTH
John