6v NiMH receiver packs are as cheap or cheaper than many 4.8v 600mah receiver packs. I just ordered a Venom 1200Mah 6V NiMH battery:

http://www3.towerhobbies.com/cgi-bin...?&I=LXHUJ2&P=7

...for a Tower Kaos 40 build I'm (planning on) working on. At $12.99, it's as inexpensive as most any 4.8v NiCd receiver battery I could find.

Servo City still has Futaba 4.8v 600Mah receiver batteries on sale for $6.99 each. If I wanted 2 or 4 of them, it would be worth putting an order together. Just one of those would cost as much as the Venom battery after s&h.

The folks at Hobby People often put receiver batteries on sale. I bought one of these Hi Energy 1600Mah 6v NiMH batteries with my last Hobby People order:

http://www.hobbypeople.net/gallery/233836.asp

They were on sale for $11.99 at the time. Hobby People often has good sale prices on these kinds of batteries.

If you can't get a really good deal on basic 4.8v 600Mah receiver packs ($8.00 or less delivered), there really isn't any extra cost required to jump up to a higher capacity, more powerful receiver pack.