Search:

Some triggers are harder to work with specialy on the cheaper rifles. Those are cheap for a reason.
Some time it is cheaper to change the trigger with a timney than mucking around for hours....

You are looking at spending $600 at least for a good scope.
I am not sure if timney makes a trigger for the atr, but if they do it would probably be a few 100 s to get it here and installed.
Maybe...