[Jack]

Denton, you're right that practice with a rangefinder before hunting will help your range estimating.
Another thing you do, if you're smart, when you use a rangefinder, is use the rangefinder before the game appears. When you're in a spot for any length of time, take out the rangefinder and check the range to a few places, like "ok, that clearing is 300 yards" "that hilltop is 225"
That way, when game appears, you are likely to know the exact range without having to use the rangefinder on the game itself. Much quicker that way.
Model 70, I've been hunting woodchucks since 1955, and doing a lot of range estimating. Buying a rangefinder taught me that I was nowhere near as good at estimating range as I thought.
I would strongly suggest you get one- I know it may not be easy, financially, but it's more important than another firearm, for example.
IMO, Leica makes the best hand held one.