The Lipo 540i kit has the best battery upgrade potential, if I had to pick just one. Since it just has a flat pan chassis, there is no limit to the kind of battery you can run, as long as it fits; lipo, 2/3A, SC, AA (for stock motors) or whatever you might have lying around. It is the only kit that works well with 2/3A cells, since the other kits have the battery cutouts for the larger cells. Although if you have a pre-made 2/3A pack, it will fit any of the kits fine. We just don't recommend running 540 motors with 2/3A cells. If you just want to stack SC cells, then the Gen2 540s would be the best since it's the widest and might actually fit that many cells (although I don't know how to do it and make it look decent). As far as most motor potential, the 4-cell 540r kit hands down since even on 4 cell, with a low-turn modified motor (<10T), it can get pretty crazy.
Giving discounts on shipping to select people is kinda a pain with PayPal since it doesn't really allow you many options with shipping other than a flat rate. It's $69 cheap enough?
Well, we charge a flat $6 for Priority and it actually costs us $6.25 to ship since the rates went up, but I never got around to updating the site. So how about that sweet 25 cent discount right there?
Actually SteveM, since you're in Canada, we usually ship EMS which is expensive but it's insured, we can do Global Priority mail, it's about 1/2 the cost but it's uninsured. If you're used to getting things from the States though, it may work out for ya.