Have you looked through either kowa in the field? Just curios, as they are all great scopes.
Im not Bwana, but I have used them. The 77 is a better scope, optically, and the Kowa Prominar WA eyepiece is better than either of the ATS/STS zooms.
To the OP, if it were me, I would jump on that Kowa deal, if it is in great shape. Already having the WA eyepiece, you could get the 88 body later if you want max performance, too. Leaves a lot of room in your budget for a great tripod and head.
The ATS 65 is really light, and a great performer too. Not many people regret getting one.
The Meopta Meostar HD is a top performer with a big 82mm objective, but it is heavier than the Kowa and ATS, and may not meet your weight needs.