Hmmmm. I'm a 1 month "veteran" of the laser wars so take it for what it's worth. If you spend untold hours on research on these forums a trend develops no matter what origin country, brand, whatever. You need to be comfortable with technology and as I said in another thread able to use and understand ohms law, a voltmeter, high voltage, motors and mechanical devices etc. Computer literacy is a plus but something you can learn (and fight with in my case). I have not seen where the in-between machines (the Chinese machine resold by a US firm/ guy-in-his-garage 2 to 4 K) have a very good track record for service. My take on this is all of these machines require technical expertise and a lot of attention by owner "hands on" on the part of the owner and having someone hold your hand beyond any more than some quick basic troubleshooting will not work. There is not enough money in profit in the 2-4 k machine for a dealer to help you for more than a couple of hours before he will realize he is not married to you and start dealing with other people/problems. At 15K+ (Epilogue) the machine can be more sophisticated with better engineering and materials and safety devices. There can be a dedicated "manual" writer and since there will be less problem machines the technical staff have more time to devote to those customers with problems and those customers are more likely to be businesses with repeat possibilities etc.
If it were me I would find the cheapest ebay machine with the size requirements you need and that is located in a warehouse on US soil, and then plan on no service, help, warranty etc. I would keep some money in reserve to take care of any problems. BUT what I did or would do is not what you asked.
One thing you have asked: I have noticed these forums the stellar service folks are getting from Marco at light object. Me I would try and get this machine for 4K from ebay and accept the "no service" but here is where I would buy under your rules:
Professional 60W CO2 Laser Engraving/Cutter machine 600x400 with power Z table
IT is another 2K than what you specified but his is the only (Chinese reseller) company I have not read anything bad about. That is his cheapest machine and I have never read a bad thing about him so I think that will be as good as you can do. OR you could buy one of the cheapies and get Marco to send you stuff to upgrade it into a useable machine.
On that last note: After having run a metal lathe, milling machine, 3d printer and now my cheapie laser, regardless of the quality of the machine or the backup, I don't see these as a "consumer product" and the skills needed require the operator to have a good mechanical/optical/electrical background and that is before the "artistic" portion even comes into play. Even just the optical will drive you nuts if you don't have a good grasp of where the beam will go when you adjust one of the screws on a mirror. A quick (AND INTELLIGENT) question to the supplier will get a good response probably from any of the various sources, but if the question is: "which way do I turn the top left screw on the Y axis adjustment to make the beam go down" well IMHO you need to go back to school and check into physics, geometry and shop class and skip the art and gender studies classes and get a better education. These are an advanced (and yet simple at the same time) tool and require an advanced mind to own as a successful hobby. If your real interest is the "art", well do the art and hire the laser. If commercial use you already bought an Epilogue and you hire someone to service it!
A month ago I didn't have any idea how these machines worked. I thought they had a laser mounted to the head. Because of my background I came up to speed on the machine part real fast. It's not at all difficult or rocket science for someone with a technical background but I really cannot figure out all the call for "backup service" for something that is as hands on as one of these are. They are to heavy to "return for service". It's not going to happen and local troubleshooting is mandatory.
I hope this was helpful? I think it's like money: Only those that don't need to borrow money should borrow money. Only those who don't need help with a laser (substantial that is) should buy a laser and as such should get the cheapest they can afford. If you have some technical expertise you shouldn't be afraid to buy any of the machines after a little research. They will all let you down, if not right out of the box, in 6 months or a year and you will need to research the forums and figure out what is wrong yourself at that time.
Now as to myself... Boy I wished I had paid at least some attention in art class, but I can "laser" a real good rectangle or maybe I can sell you a triangle? :-)