I was just on the Hobbyking web site, their hardcase batteries have just dropped in price (curses, I just bought four) and they're offering 5ah 4s batteries for £13.56. Six of those give you 42 volts and 10ah for £81. That's International warehouse (so you'd pay shipping and customs and vat).
http://hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=15521
UK warehouse (vat is included, no customs, shipping very cheap) has them at £15.16, so £91.
Of course, these are Lipos, so you'd need a Lipo balance charger.
http://hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=15521
UK warehouse (vat is included, no customs, shipping very cheap) has them at £15.16, so £91.
Of course, these are Lipos, so you'd need a Lipo balance charger.