And i forgot to mention, minicom term emulation quality sucks, even giving simple shell commands is a PITA, upgrading the whole fleet would mean bast case scenario minimum 21K USD for the whole fleet + suspension of all other activities for two months. If physical travel was involved, the cost would be increased at even higher levels.
And what is the cost of data corruption on large numbers of systems? And how much to fix that, especially if multiple systems fail at the same time? Some things aren't free. $21K in exchange for NOT having had to keep systems up to date for 4 years seems like a decent trade.
Just call up an oracle sales rep and get a price quote for a single baseline system. Put that next to the postgresql upgrade cost for your whole fleet.