Go for the used Prusa MK3S+. People used to pay a premium for assembled and tested printers. As long as you can get the printer to you without being banged up in shipping it’s good. Really shipping would be my biggest concern.

I have a MK3S+ and it just prints. I print for my Etsy shop and don’t really feel the need for a backup printer. I have 1600+ hours of printing on it. In that time I’ve had one nozzle clog and one blob. I do a little dust filter on the filament so i don’t often get clogs https://www.printables.com/@Fohn23_807562/collections/641537

I’m totally happy with just the smooth sheet. The textured sheet is supposed to work better printing PETG but I’ve been able to get perfect PETG prints on the smooth sheet using windex as a release agent.

I’ve owned 3 printers, all cheap. For what I spent fixing it upgrading them I could have bought a Prusa. More than saying my next printer will be a Prusa, I can say that I actually have one on preorder.

Also, I will never buy a fdm without a bed leveling function. No, it’s not necessary, but if you want a low frustration printing experience, it is - in my direct experience - essential. Prior to having abl I would keep an eye on every print start. With abl I send a job to the printer and check on it when I get around to it.

I’d go prusa mini at this price point. It’s a really reliable little machine, and easier to build than the MK3 and others. Enders are really not worth your time, trust me, I had one.

Just as a heads up,you claim to say that speed and size is not important, but trust me, speed and size is always important for 3D printers. Minimum size (except for unique situations) should be around 8"/200 mm cube. For speed, I think the Voron kit was (one of) the fastest ones out there. Now your budget won’t allow for one of those printers, but they are a good way to compare the ones you are considering.

I’d recommend the Ender 3, I have the Ender 3 Pro v2 I believe, and it’s been very reliable and worked right out the box. I got it on sale at micro center for $100 USD, I’ve heard they go on sale fairly regularly.

Assembly is easy. It doesn’t have auto bed leveling, but the adjustment knobs are easy to use (look up some videos on using a piece of paper and moving the X and Y location of the extruded to level).

It doesn’t have error detection, but I’ve seen some mods online that use an Arduino for this. Even with error detection I don’t think it’s recommended to print unattended due to fire risk.

It comes with a removable flexible textured print surface with heated bed. This texture helps with print adhesion by keeping the part being printed secure while printing. And for fragile parts, you can remove the print surface and bend it to help remove the part after printing is finished. This has worked nearly flawlessly for me, compared to earlier printers where people would use painters tape/glue sticks/etc to help with bed adhesion.

An enclosure is a nice addition, but not really necessary unless you’re doing large prints or really trying to push the boundaries of what you can print. The idea of the enclosure is that it keeps heat in to prevent the part from warping as the extruder moves up along the Z axis. For small parts the heated bed will provide enough heat. You can build one out of plexiglass and 3D printed brackets, or an ikea coffee table (look online for examples).

I just upgraded from Monoprice Select 3d (not what you want) to an Ender 3 S1 and am super happy. I’d recommend the S1 over V2 for you if you think you might want to ever print flexible filament

I got mine for $299 USD on Amazon

You’ll want an enclosure if you want to contain smell or if you want to print in ABS (of any size, as drafts will fracture the print before it cools)

Speed is not important? Are you sure? Is this your first printer? I though that too at first, but trust me, you are most likely going to want speed more and more once you get going. Also, 3D printing is pretty much synonymous with tinkering unless you have some sort of business model in mind, but if you do… (see comments about speed).

My take, go with lightly used mk3. Market is primed for two reasons - first, in US at least there is just less of a sellers market lately for anything used and with recent Mk4 release people are looking to sell to upgrade.

Wish you luck with whatever you end up with and have fun and don’t be afraid to tinker!