My experience with Alien Power/Bruno was horrendous and i strongly recommend to avoid any/all items they sell. The short short story was an 8s dual motor ESC that *cannot* handle 8s voltage (is not an 8s ESC). Took over a month to get a refund and was extremely unhelpful until i threatened to have CC dispute the charge. He changed the description to 7s dual ESC afterwards, which i do appreciate so others don't have the same experience. Not even going into the quality of those ESC's (i was new and didn't know better).
I would go with Enertion in a heartbeat. Quality components every time i've gotten something and i've seen him offer kick-ass-customer-service on a couple occasions. Replacing items with speed and just going the extra mile in general.
Option C would be some thin Lipo packs from HK. Not the same as the space cell, but quite a bit $ less. I have some for one of my boards in progress - They are around 22mm thick. I'd start digging for the specs on lipos and determine what's your max thickness you want.
GL!
