The last "North America" base/city former (If you don't count the RID Fort Max that didn't happen),
it would be Microverse bases from Beast Wars. Mind you it was for a completely different playpoint so if you ignore that then it's not a trailer base, then it's the Battlestar Trio of Star Convoy, Sky Garry and Grandus in 1991.
Fortress Maximus originally retailed in the USA for $99.99 USD and in Canada (atleast according to my Consumers Catalog X-mas 1988 which was normally a little over priced). He was $169.99 Canadian.
I have 2 MIB reissue Star Convoy (One to open, one to keep sealed), and I have 2 loose vintage Micro Hot Rodimus but sadly I want to get a complete MIB Star Convoy circa 1991 one day.