Hi Donnie,
It sounds like you have progressed nicely. After 25 planes and 5 helis, you are now in the category that my wife calls "obsessed".
Your experience with the cost of LiPos is normal and the LHS owner made reasonable recommendations. The ThunderPower brand name is a good battery and you should always balance the packs... preferably during a recharge.
I would stay away from many of the cheap LiPos sold on eBay and stick with a brand name that is backed by a reputable distributor.
Here are just a few alternate 4-cell pack choices for the ElectriStar.
[link=http://www.hobby-lobby.com/polyquest.htm]PolyQuest 3300mAh, 3700mAh, 4300mAh or 5000mAh packs[/link]
PQ33004 "Twenty" 4 Cell 14.8V 3300 mAh LiPo Pack ..... $ 158.90
PQ37004 "Twenty" 4 Cell 14.8V 3700 mAh LiPo Pack ..... $ 167.90
[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXMDN4&P=7]Great Planes LiPo 7.4V 3200mAh 20C 2-cell Pack[/link] for $80.
[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXNWV8&P=7]Kokam 3200mAh 4S1P 20C LiPo Battery[/link] for $172.
[link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXNLK0&P=7]Team Orion Avionics SLPB 3200mAh 14.8V 4S-1P LiPo[/link] for $200. Note that this is the same Kokam 3200mAh cells as above.
Good luck!