I know this may sound stupid, but how is your eyesight? The reason I mention this is because 50 yards seems to be the number for me also. With open sights I do good up to that number and past my groups open up a lot.
That is the reason most of my rifles have scopes on them. If your rifle holds good groups at 50 yards it should do fairly well at 100 yards. As far as ammo goes no reason to give up your "best bud".
The answer to that one (for me anyway) is reloading. It doesn't cost much to do reloading on the cheap. I started out with the Lee Anniversary kit and reloaded some very good ammo.