You should be able to get 4 or 5 flights out of a freshly charged receiver pack, many more from the transmitter.

Crashem was right on the money on the ESV meter. You can buy one at Tower Hobbies for about $15 to $20, and it's worth every dime. Check you receiver pack between each flight to be safe.

You should eventually buy a charger that is capable of "cycling" the packs. That means discharging, then recharging, while keeping track of the bpacks capacity in milli-amps. A 600 mAh pack should be tossed when the capacity drops below about 580 (in my opinion), because the danger of a cell failing grows higher.
Dennis-