NON user-serviceable ET-2400 ink pads, information needed.

A lot of it depends on the frequency of "maintenance" being run on the printer (auto and manual). Otherwise, they usually last ~5-6 years these days with the internal pads (used to be 10-15+ before the 2010 black cart printers happened) unless you really run them hard and run the page counter up to 20k+ pages in 1-2 years. If you run the maintenance on the printers a lot it still hurts you a bit but at the same time, regular maintenance will not do much harm as the tolerance is built into the printer.
However, power flushes nuke your waste box service life drastically so much so it's a NUCLEAR OPTION to AVOID!!! Never, EVER utilize power flush!!! FULL-COLOR PAGES TARGETING THE ISOLATED COLOR DO LESS HARM! It was originally sold in Walmart and Target, so that should give you an idea of who is usually buying them.

Epson cost is simple: as much as a new printer, or you're SOL. Usually SOL; Epson often denies HW service when you ask them to fix it due to the parts being EOL, or "too expensive". They would rather give you a one-shot reset to get more out of the pad but once that's done you can't reset it again. However, since the ET-2400 is derived from the "chipped" box printers which were designed to be replaced, it's accessed on the same service panel as the serviced ones and only needs a Phillips driver. However, you need to reset the counter which isn't always possible, or it takes years to open up the reset to 3rd party tools like WIC reset utility (some may never be resettable outside of Epson). Epson used to have somewhat regular tool leaks where if you can find the appropriate adjustment program+keygen, it was possible; like Canon, I suspect Epson has moved this to the cloud logins to prevent leaks and encrypts these tools so we can't hack/decrypt them.

I use laser printers for a reason, despite color and B/W models that aren't junk being $400+, or if I get a deal on a used high-end model like a split drum/developer Lexmark CS with a low page count for a reason: This isn't a problem. However, they're more expensive to maintain than a $250 ink tank like this Epson and need more consumables (drums, toner, developer. Some even consider the transfer belt/fuser "maintenance items" at 100-150k pages). Yes, these may require a truck or 2 people who can lift a heavy printer with how big they can be in some cases (others need a box truck like the copiers with print support or printers the same size as copiers). The best ones in this "lots of consumables, cheap to run" are the Lexmark CS/CX series where they split the drum, toner, and developer (they mention the fuser and transfer belt in the supplies page, but I think the split CS series is the "quality is unsatisfactory" outlier) or even the WorkCentres from Xerox. However, all of the major manufacturers sell these but you need to seek them out.

Here's how big some of the "compact" ones are. They're workhorses, but fail the "consumer convenience" test since they're not like an Epson EcoTank where you take it home and setup the unit, you need a table that can handle it or a printer cart:

Disclaimer: I develop and sell solutions to this specific problem under the Printer Potty brand so I have a commercial interest but I'm here to answer the question, not to sell. If you want to look up more about the Printer Potty solutions, you'll need to go searching.

Summary:

• ET-2400 is compatible with the WICReset app meaning that the waste ink counter can be reset (USB cable required)
• The OEM part reference is: 1749772 Porous Pad Assembly
• Third party replacement parts with and without the plastic holder are available.

Longer Explanation

Right, that out of the way, Nick is correct. The newer ET2000 series are still being produced without the chipped maintenance boxes that other more expensive printers (eg: ET3000 and ET4000 series) now seem to have as standard so you do need a waste counter reset to be able to clear the waste counter and the "pads at end of service life" error that it creates. I checked and WICReset is currently compatible with the ET-2400 so that's covered.

Thanks to a post from Elizabeth White (below) I can confirm that the ET-2400 seems to use the same porous pad assembly (Epsons technical term for "waste pad holder") as the ET-2700 to ET-2720 and looks like this:
https://www.octoink.co.uk/product_images...

Just as an aside, it is also possible to fit external waste ink kits to these printers. As some of the comments indicate that these are being used a lot for dye-sublimation printing (which is incredibly wasteful when it comes to ink) then an external waste ink kit is definitely worth considering for that sort of usage scenario.

If multiple resets are anticipated you can also purchase WICReset keys cheaper if you go to 2manuals.com as they offer discounts for bulk purchases. You may also find somewhere selling the official Epson adjProg utility/app although I haven't used one for close to 8 years now and can't vouch for how safe and/or reliable they (or the sellers) are now.

Hope that offers some hope for those of you who had pretty much given up all hope with this and I'm happy to answer questions on the waste ink side of things if anyone wants to comment here or via my main company details (I'm sure you can find them if you search).