we are at over 21oz for the batteries alone compared to under 7oz for the LiPo!!!
You don't have much choice. That's the problem with NiCad and NiMH vs LiPo. You might be able to find a NiMH battery that will be do a little better but it's not going to be anywhere near as light as the LiPo. I have a GP Super Sportster EP that came with a 7 cell NiCad pack that weighs 13 oz. The TP 3 cell 2100 mAH that I have weighs 5 oz. With a NiMH I might save a few oz. over the Nicad but I'm not going to approach the 5 oz. of the LiPo.
The only thing you can do is check specs on the batteries for capacity vs weight, keeping in mind that the discharge current needs to be enough for your application.
Mike