i havent had any leaks with the t-top and the majority of mr2's have a/c ... it depends where they live and how often it rains in the area they are from... assuming you live in america.. the last production year was in 1995 so unless you import one from japan or something of the sort you are stuck with 91's to 95's (94's and 95's both being quite rare)
with $6,000 you should be able to find a pretty good condition 93 turbo which is what i would most likely recamend getting... the price spikes over $10,000 for the turbos at 94 and 95 for the reason above
there are plenty of mr2s on ebay.com (obviously), xcars.com, autotrader.com, and mr2oc.com (in the mr2's for sale section)
gl on your purchase and if u find one, welcome to the mr2 community