Yes, 100 credits is $1.
The best putter is the Ping Redwood ($6) and the easiest putter is the Spider ($4). To make the best putter a bit easier, you can combine it with GI-D balls ($0.50 or so) that slow down its meter. That's what I'd recommend. (Or, buy both putters & swap them between rounds; that brings more variety to the game.)