I live in Gatineau and there's not anyway near as much options as if your are around MTL nor was I willing to build my own pack. If this is overprice, then it's pretty sad because I had saw much higher prices than that when I was looking.
Make a search for your battery pack product # in google and add "canada", that's how I was able to find the somewhat cheapest option.
Building your own pack (for most UPS) is not hard... For these UPS it is very simple... For the SUA1500 you just removed 4 nut&bolts (2 hold the main connector to the battery (1 to +, and 1 to -). And the other 2 just hold a small fuse to the back tabs...You get the 2 new 12V18Ah batteries, put a small piece of double sided table to hold them together on the sides, and reattach the same cable/fuse and 4 nut&bolts... There is no soldering/spot welding or anything else, like when rebuilding tool batteries
For many of the other UPS (smaller and simpler - often use 12V 7Ah SLA), they are often just a matter of pulling of the cable which is connected to the battery with a push tab, and reusing it...
At $155 for the RBC7 (which is used for the SUA1500 and other larger units).. You can easily save $65 by reusing your cables, and battery is identical.. Now if you don't want to bother with 4 nuts/bolts, then yes, $155 is a fair price for an original RBC7, with all the cables.
Magnacharge, last I bought from them a few months ago, was selling the 12V 18Ah batteries for my old SUA1400, for $43 each if memory serves me correct... Picked up 2, and no worries about old stock, considering all they do is batteries...
I agree that outside of Montreal/Laval area, your choices are somewhat limited. I've seen cheaper batteries, but when you read reviews of some of these vendors, it is horrifying sometimes.. And often shipping costs (due to weight) often make the deals, useless.