I've purchased a number of 700Mah Ace Hobby 4.8V NiCd receiver packs from
http://www.infinitehobbies.com. They have both the flat and the 2x2 types for $9.12 each.
ACE2906J - Futaba connector, flat pack
ACE2906S - JR connector, flat pack
ACE2907J - Futaba connector, square pack
ACE2907S - JR connector, square pack
This is the best deal on standard receiver packs I've come across so far.