The original bottle will last years. The replacement bottle will probably go through several price increases until you buy it, and then that will last for years. Not sure if you will still have the printer at the end of the 2nd bottle, but if so, the 3rd bottle will be even more expensive than the 2nd. The nominal difference, it is no use getting the non-Epson one in case the formula is anything different that messes anything up during the initial or extended warranty periods.
The question I would ask is about ink savings. But given issues with generics, more head cleaning, and head replacements, just stay with the original Epson ink, you'll break even with fewer issues and headaches.
The only savings left to explore is taking power from your neighbors to run the printer, and buying media in bulk.