Late 2014 Retina 5K iMac Random Shutdowns

Hi all,

My late 2014 Retina 5K iMac is shutting down randomly for no clear reason.

I've reset PRAM and SMC, with no good result.

Hitting the power button does nothing until you physically remove the power cable and wait 30 seconds before plugging it back in then powering on. You start to work again, and pray for how long it lasts until complete shutdown again! VERY, VERY FRUSTRATING!!!!!!

I'm outside of the 3 year AppleCare I bought with the unit so I am wondering how much it would cost Apple to replace the Power Supply as that is obviously the culprit here (there's PLENTY of documentation of this happening out there!)

There's loads of tutorials on how to do it yourself and seeing as though I am 6 hours return train ride to my nearest Apple store I'm leaning towards tackling it myself (despite being scared stiff of that screen and getting it off and back on again!!)

What would others suggest I do?