For the best power-weight-cost, look at the LiPoly batteries used by R/C cars. There are some pretty big ones available, which you could gang together for quite a power pack. Not as cheap as SLA batteries, but about 1/8 the weight per equivalent amp/hour. Aside from their price, the only downside is that they have to be charged correctly, or else they can overheat and catch fire.
11a/h 14.4v LiPoly = 1.8 lbs @ $300
18ah 12v SLA = 12 lbs @ $50
(You'd need at least an 18ah SLA batt to give about the same running time as a 10-11ah LiPoly batt because of the 11.0 v cutoff voltage in many radios. An SLA battery will hit that at about 50% of its rated time, whereas the higher voltage LiPoly batteries will stay above 11.0 v for a much greater percentage of their rated time. Another advantage of the LiPoly batteries is they can be discharged at 30-50x their rated capacity. This 11a/h battery could comfortably provide 200a discharge current without damage so the 20am required by a Ham radio should be no sweat. The same doesn't hold true for an SLA battery.