I work in "the industry" and have designed and built many printers (years of experience with them), and one of a few who have built what are called large format printers.
You need to first understand, a 3d printer is not a toaster. Yes, you know it means you cannot just press a button, but most fail to grasp the learning curve involved and the shear amount of troubleshooting and maintenance involved. They are literally a hobby unto themselves and people REALLY do not understand that. These have FAR more in common with a CNC mill than they do printing or even woodworking, that includes the amount of trouble they can cause and the skill required to get good prints from them.
Also, I don't know what size keyboard you are working with, but anything over 60% gets sketchy on most printers, I built my first big one (several years ago) to handle a TKL
laid flat and it's still one of the largest around. Another thing people forget with large printers is that they need a lot of space... LOTS of space. I have found peoples eyes are very much larger than their desk. Mine barely fits on my desk, and any larger it would require a dinner table to support it. No big deal you say, but it's not like you can just put it in a closet when not in use, this is a big machine.
Anyhow...
Chinese printers are exactly what you would imagine. Some are okay, some are pretty good, however, MOST are designed by someone and run though a couple prints and sent off to manufacturing. Worse, of the ones I have seen, most arrived with at least one part being broken. Granted, that is one reason it was brought to my attention so I could help fix it, but I'm not alone in this and I was far from impressed with parts quality on the cheaper ones. Even the better ones almost always need work to make them work well.
Some have even shocked people, and some simply didn't even function out of the box. 3d printing became a race to the bottom, and all rules for quality went out the window. Bigger printers are no exception. They also have HORRIBLE support.
At TP mentioned, they are often warped. Even under the best circumstance, something thin and flat will have some twist. You need structure to flatten it back out (I.E. a case). This is especially true with plastics like ABS. Plastic shrinks as it cools, some by a little (approx. PLA 0.3%) and some by a lot (ABS 3-7%). This causes prints to shrink and warp, but it also causes the plastic to pull itself off the bed. Some of the plastics are also toxic (ABS and some nylons in particular) and should not be used without a fume extractor, some are safe (PLA), for the most part. Some, like ABS are also EXTREMELY sensitive, people erect cardboard walls around printers because simply opening a door can cause a draft that causes it to delaminate. No, I'm not joking, ABS is a nightmare for many printers. You need an enclosed printer to really do ABS and you still have shrinkage and warping.
As for a printer, the Prusa I3 is about the cheapest you really want to go.
Some will argue some of the clones are better, frankly, no. Yes, these is a few good clones for less, but they lack the support you need as someone new to the hobby, yes hobby. The Prusa has features that will greatly improve the likelihood of a good print and their support system is excellent. It also prints good, where I think it fails is in longevity, it has wear issues some other designs do not have, however every design has tradeoffs. This is not a slam on Prusa, it's one of the few printers I will recommend to people, and certainly one of the cheapest. If you had some experience, one of the clones could be a bargain, but if you are just starting and do not have access to help locally, the Prusa is the cheapest good option. You may say I can just work through it, and this is true, but do you want to have a working plate next week, or are you willing to spend the next 2 months learning before you get a good, usable print and what is it worth to you?
Lastly...
A 3d printed prototype is great, it can find flaws quickly and help you correct them, cheaply. However... Your 3d printer does not have the same tolerances as a laser, water jet, or cnc mill. So, even if you get everything right on the printer, it does not mean it will translate to the other formats. It can reduce the time and prototypes required, but do not expect it to come out perfect just because you tested it on a 3d printer first. At least not without some experience.
So here is my advice.
If you want to play, and make a case, get a printer, but don't expect a working, functional item right away. This is engineering. While a plate may seem simple, it's a whole other aspect when you have to concern yourself with shrinkage, warpage, tolerances, along with making sure your temps are right, extruder didn't jam, did something come loose.... Talk to many people with them, and unless you get a high end kit, it could be months and several kilos of plastic before you get anything remotely useful.
If you just want a plate and want it cheap, take it to a laser cutter or waterjet and just get it done, a few prototypes should give you all you need before a final product is made and those will likely be less than the cost of a decent 3d printer. If you plan on manufacturing it, make it clear to them that there will be a bulk purchase once completed, you will get it faster, they will often make suggestions on how to make it cheaper and often charge you less for the prototypes (but don't lie!). Remember, making stuff on a 3d printer is cheap, but only if you already own it.