

FWIW, I bought a new Ender3 as a kit not too long ago, it was $150 IIRC. And by being forced to assemble it, I learned a good bit too. It might be worthwhile to watch their store & see if they put it up for sale again.
The only upgrade I’ve done that I really felt made a difference was buying an enclosure for it. Nothing fancy, it’s a fireproof bag over an aluminum frame. Even more than controlling the temperature, it also keeps it dust free when not in use - that’s probably the biggest win for me.
As for buying the used one - these things do wear down. Start by checking the feed gear & the PTFE tube. If the filament feeds well, then also check the belts, rollers, & nozzle. Those are really the common wear items imo. Perhaps obvious, but make sure the seller gives you a copy of the slicing software (should be free on their webpage) and also the little USB-A to Sim card doo-hickey that you need to move files back & forth.
Mildly related - I vividly remember back in the 90s on my drivers test in Florida, it was illegal to have a screen facing the driver. Period. Now, what they were aiming at was making sure the driver wasn’t watching a portable TV while driving. But the center console screen in modern cars would 100% qualify. Heck, mounting your GPS or cell phone to the dash so that it’s hands free would still be illegal by that law. So I have to assume something in Florida’s driving laws changed. Always been curious what, but I moved away shortly after then, never bothered to follow up.