Well, here's some food for thought.
The MSRP from STAR on their web site for the UMP is $385 USD.
http://starairsoft.com/List.htm
WGC sells the STAR UMP (pre-order) for $280 USD. War 4 has the same price, as well as Boom Arms.
So that would be about 73% of MSRP. One could extrapolate that WGC will sell it for around the same ratio, so around $470 USD???
In addition, Aqua was able to get the UMP for 42,000 Yen, so that comes reasonably close to the $385 MSRP.
This reasoning doesn't always work though. Maybe the $385 MSRP is an error, as it's not on the actual product page. Also, Echigoya International jacked the price of the UMP to $500 US. About a 30% increase from the MSRP. They also sell the STAR M14 for $800, a 12% increase on the MSRP of $712.
In the end, I'm optimistic that it will be within 30% of the MSRP + the markups from the Canadian retailers.