What is the best 3D printer for under 200 USD?

Well, $200USD is not much to play with ... you're probably going to have to compensate a bit by tweaking and upgrading as you need. The Ender 3 Pro is often recommended as it's rather "open" in design and has many customisations - but it's effort and tweaking that you need to have the time to put in. Others get entirely frustrated and claim it to be the "worst" experience in ironing out prints that don't come out straight (because of incorrect assembly) or problems with under-extrusion (due to damaged/worn parts), etc. If you want it to just work for a more commercial purpose, you're probably looking to spend at least 20x as much ...

Carbon fibre-based filament is a difficult thing to print. It's going to need a hardy nozzle - the brass stuff that's normal for low-price printers is going to wear out, so stainless steel or better is recommended. That in itself is not a massive expense but it is a little hassle. The next issue is that you need to get your bed to about 80c, which open printers like the Ender 3 Pro may not be able to maintain especially in a room with some airflow going - so building a "hood" or "box" around the printer to retain the heat is highly recommended. Add to this that you also need a print temperature of about 250c or so means that you're probably pushing the upper limit of the cheaper printer's all-metal hotends.

PETG is a little more forgiving of print temperature, but the bed also needs to get to about 75-90c, so again, it might be a bit of a push for the printer especially in colder climates.

Quick printing is very much dependent on a few factors - the size (volume) of the model, the complexity of the geometry is a big one. For the most part, cheap and quick definitely don't go together and many of the cheap designs aren't rigid enough nor well designed enough to print well at high speeds, even if it can. For example, my printer is advertised with a print rate up to 100mm/s, with a recommendation of 60mm/s. What I find is that anything above about 40mm/s causes noticeable loss of fine details because the head isn't following the path just right as the play in the belts and frame start to also induce "shimmer" or ripples in the walls. How many "days" a print takes really depends on a lot of factors - download some slicing software (e.g. Ultimaker Cura), select your intended printer, change a few settings and run your model through that to get an estimate of print times.

- Gough

What would be a reasonable budget for a 3D printer GL?

I'd say $400-600, and then at least you can consider resin printers as well as filament.

I'd say $400-600, and then at least you can consider resin printers as well as filament.