The chains themselves aren't what wear out....it's the tensioners and plastic chain guides that deteriorate.
It all depends on how much you get an engine for. They range in price depending on mileage. I got my 1,000 mile 2006 engine for $1500.....all this yards 4.0 SOHC's were the same price....so why not get the 1,000 mile unit. Did the swap a few months back for the following reasons: timing chain rattle as worse as its ever been, punk teenager driving it the last 110,000miles, it sucked down muddy water down the intake on 3 maybe 4 occasions and it internally had suffered.
Check out www.car-part.com
. It's where I found my engine. It's a website catalog of a crap ton of junkyards and their inventories. I wanted the newest year possible....less likely of a chance to suffer from the timing chain faults of the early model SOHC's. You may need to look up 2004+ instead of 2003....they seem to be seperated in junkyard computer systems.