Actually, mine did come with a little juice in them (kinda unusual.. maybe they did a partial charge to verify the pack was wired correctly?) but it certainly wouldn't be worth buying new ones each time
It's really not very hard to make your own charger. Buy an AC-to-DC adapter rated between 300mA and 800mA, depending on how fast you want to charge (safety vs. speed) and get one rated between 3.0v (for two cells) and 4.5v (for three cells). I got a
Radioshack Adapta-Plug so I could change the voltage. I also got a
Hobby Leads adapter for it and soldered the two free wires directly to a charging base from an old clone charging pad, leaving the adapta-plug end sticking out a few inches. Now I plug the two ends together and charge away. Otherwise, you could just strip the wires on your adapter and wire it that way.
If you don't have a spare charging base from an old controller or something, I've also done it where I left the charging base in the controller and drilled a hole in the case to run the wire through to the base, then snipped the existing charging wires from the controller. You can connect the adapter directly to the controller then disconnect when the car is done charging. You'll have to time it yourself instead of watching the controller LED, of course.