Replacement Gateway laptop batteries

I have a Gateway MX7120 laptop (successor to the MX7118, surprise, surprise). On the Gateway site there are six different batteries for this laptop, all from Dynapak (sp?). Supposedly, the only differences are how long each holds a charge. I'm currently lucky to get 2 hours out of one just surfing and typing.
The current battery is listed as a Dynapak 100440, 8 cell Li-ion.
Part numbers: 101339, 101340, 101341, 101343, 102801, 106828

Where else could one get a decent replacement / spare battery for less than the arm and a leg Gateway want? Would I want to go elsewhere?

Thanks!