Im looking to buy a new .12 rear exhaust engine. I have been running ab OS max 12TR for about 3 years now and it is now only starting to struggle so i figure i will just get the same engine again.

What would be the cheapest place to buy this motor? I have seen them at RC-mushroom for $115USD for the 3 port or $179USD for the 5 port. Would RC-mushroom ussually have these motors in stock and how long do they ussually take to deliver?
Also how much of a difference would there be between the 3 and 5 port versions of this engine?

Any other places people know of with cheap engines or any competitive places here in australia?