Yeah, you are better off for sure getting the latest lipo packs for your R/C's. However I don't see why you think lipo's are cheaper for an ebike? Do you mean Turnigy/Flightmaxx packs? If so, IMO, I would not go that route, too risky... those packs aren't quality built, you will most likely run into problems in a 2 years or less. I know Metallover is using them, but I can't see them being a long term investment, no offense metallover!

Building A123 packs is surprisingly easy and fun actually, you just have to be careful not to short them out...
You are right, 48 cells is the number of cells I would be using if my brother goes the A123 route, 12s4p pack, split wired for charging. I have calculated that would give a bike a conservative ~18 miles range at a decent pace, say 35- 40km/h.
If not A123's, the the
Headway 38120 10Ah cells.
HERE is the A123 10Ah cells, not much info, the 10Ah cells specs are on the bottom. Go to A123 Systems website for a pic of the cell, not much to look at though.
I am hesitant on those cheap ~$4.5/cell A123's from eBay (China) as well. We don't really know if they are genuine or not, if some cells could be dead upon arrival, whether they are used, so I don't know yet, still trying to find to people who have used them.