I've researched most of these same models, and like you, I've eliminated several because of the weight. Have you looked at the Dolphin Triton? From what I've read, it is supposed to be similar to the Pentair Prowler 830 and the Dolphin Premier and Dolphin DX6, however, it is only supposed to weigh 19 lbs. About $300 less that the Dolphin Supreme M5/Dolphin Oasis Z5/Dolphin Triton Plus.

I found the information on this website to be very helpful to identifying which units are similar, but with different branding,
http://www.sunplay.com/blog/the-trut...t-telling-you/