I'm in Canada and I only use Panasonic BD-R DL 50GB discs for long term storage (I need the space, 25GB is too small for video files). They are not anymore expensive then anywhere else in the world. The key is where you are shopping for them. There are only two places I now purchase my Blu-ray media from:
• Amazon.ca here: https://www.amazon.ca/Panasonic-Blu-ray-Recordable-Spindle-Printable/dp/B01HJPZCLA/
use JP-Gate and if you need them in a hurry get express shipping.
• or eBay.ca like this one (currently the most affordable for the 50-disc stack): http://www.ebay.ca/itm/New-50-Panasonic-Bluray-BD-R-DL-50GB-4x-Speed-Dual-Layer-Inkjet-Printable-Discs-/142024647597?hash=item21115423ad:g:5qkAAOSwnNBXX63o
Again use express shipping if you need them soon.
eBay seems to be a little more affordable right now. It used to be the other way around. If you need fewer discs then just search eBay using the key words "Panasonic BD-DL" and you will find lots of options for purchasing smaller amounts, but they cost more per disc, as a rule.
If you care about your data at all, you won't use anything less then Panasonic or M-Disc. I have had zero issues with data Integrity so far (burning them since 2011). If you keep your high quality discs in a decent environment, they will take care of your data.
If you have the money and need the space more then money then M-Disc BDXL is the way to go. Seems to be the best triple layer there is.