Check out LASORS sections F1.4, F1.5 and C5. If you let the class rating expire, it's an LST instead of an LPC but since both have to be with an examiner, the practical differences will be minor. An LST will probably be a longer flight with more exercises thrown in, plus there's supposed to be an oral exam and maybe some more paperwork. The differences are only becoming major if you reach the five-year mark.
As far as the membership fee is concerned, most clubs require this on a yearly basis. So it doesn't really matter whether you join now or in a few months time.
For me personally, I would prefer an LPC over an LST but mostly for ego reasons. I did not get the license to simply let it lapse two years later. (Of course, a revalidation by experience would be better still.)