That's one of the good things about the International Clarinet Society; at their yearly lovefests all of the major manufacturers and many of the minor ones and dealers show up with all of their horns currently up for sale. Without attending these for five or six years back in the 1980's, I never would have had an Ab clarinet experience (not that it was worth it, mind you).
Regarding the basset horn and basset clarinet, unless you are planning to get into obscure Mozart stuff, I'd not sweat it if I "missed out" on either one. As detailed above, the basset horn is part (albeit a very, very small part) of the classical "rep", and 99.9999999% of clarinet players will never rub up against a need to use one. Put another way, I'd buy a bass sax before I'd bother with a basset horn.
The basset clarinet was "redeveloped" when the controversy over the "original" form of the Mozart Clarinet Concerto was being resolved back in the 1970's. At that point, both Selmer and Leblanc started offering (on special order at that time) a "basset' clarinet, which was nothing more than an A clarinet with an extended lower joint to descend all the way down to low C. Lots of extra weight, a very different "center of gravity", and not at all the sort of thing for anyone but a clarinet specialist (or a clarinet nut; there are a few of those as well) to be owning. Put another way, I am an indifferent oboe player at the very best, but I would shell out money on a professional English horn before I would worry about a basset clarinet.
But, if you are intent upon the basset experience, this year's conference of the ICS (which is going to be either in Kansas City or Saint Louis) is an excellent, centrally located opportunity to do so. While visiting the vendor's showroom, you'll also get to have the unique experience of hearing fifty clarinet players (almost all soprano, nat?rlich) playing at once, all on a different tune.