The only way that makes sense is when you (and your buddies) can order over $75 and get free shipping from one of the companies on the internet.
Also see if they sell a higher capacity AH battery with same footprint.
If you cannot get free shipping, new a new UPS on sale.
Batteries are fairly heavy for shipping costs (consider it's made of lead).
Try sourcing them locally first, and if that doesn't work to your favours, get them online.
My local supplier can get them for me for 17.85CAD each, local pick up of course.