I put plenty of coins in games back in the day. The fascination with dropping coins into the game long ago wore off with me.
The only game I have that isn't set up for free play per se is my Pinball Pool. It has a Pascal Janin board in it which allows you to set free play-it sets the credits at 99 and they never change, but you don't get to see the credits go up and down, so I rigged the coin return button to trigger the coin switch to add credits when I run it down to 0. Other than that, they're all set for free play.