I seem to recall that one of the major differences between those 2 incarnations of the explorer, was that the SE pro. had VCO all-metal pinpoint mode (which made for a more-pleasant audio in that mode). But since most people just criss-cross to visually "x-marks-the-spot", I don't think that made the SE pro. any better (IMHO).
The Explorer II has a reputation of the sweetest sounds. A bit more audio difference between a silver dime to a copper penny, for instance. So the Exp II remains very popular amongst all the incarnations. If you saw an Exp II with probe for $500, that's an excellent deal! The sun-ray inline probe ALONG can fetch $150 or more.
that seems like a very good deal. Perhaps I'm "behind the times" in the market-resale "going value". But it seemed like they used to fetch $600 or more with probe. Perhaps with the advent of the ctx 3030, some guys (who always have to have the "latest greatest") might have put theirs II's on the market, thus dropping the fetching prices somewhat. Still though, presuming you don't need the water/dunk proof machine, the II is going to be every bit as good as the CTX for land anyhow. I know the ctx die-hards would debate this, but .... others will say they don't do any better for deep turf hunting, than the Exp. II afforded them.
As far as water hunting I am going to keep my atp for that. So hopefully I will have enough in my arsenal to cover just about every scenario I run into.