PAC-MAN MUSEUM+

This achievement sounds daunting at a glance, but with my solution it should take you 4 to 5 hours from scratch. Pac Motos 1-1 is the way to go for this, seeing as you can finish the level at around 5-8 seconds on average. Once you get it down you can start to get times under 5 seconds, and my personal best as around 3 and a half seconds. The faster your time, the more coins you get. Below is a video I have provided of the farming in action and the results at the end of what to expect after about 30 minutes. From what I have gathered, the maximum you can earn is 10 coins per level completed, but even the slowest runs give 4 or so coins. The average is around 6-8 coins.
EDIT: TA user Not MJC suggested to use 3-1 but regardless u=you should be racking up coins quick.

This method is in level 3-1 of Pac-Motos, which is in the free cabinet that doesn't cost any coins to play. Below is a video I made showing the technique. Hold up on the d-pad while it says "Ready" (you can skip the ready screen and part of the clear screen) so you start going immediately when it begins, then as you're going past the green ball to the right you want to tap right on the d-pad while still holding up, making you briefly go upper diagonal right. You don't want to hold right on the d-pad for too long, just enough to get mostly into the enemy lane. Doing so will get you a time of 3:93 and the max of 10 coins per run. As long as you're under that 4 second threshold you'll maintain the 10 coin gain for this map. And again, you can skip the "Ready" screen at the start to go even faster, just be sure you're holding up on the d-pad before you do it, otherwise you won't get the 3:93 time.

I was originally doing the 3-1 method posted by Not MJC in the comments of the guide posted by DubstepEdgelord, but eventually I tried going up instead and discovered this technique. Definitely check out the other two methods from the two users I mentioned above if you're looking for other strats.