Totally agree 3000 USD is way too much money for this machine.
The frame looks fine, it can handle some light milling operations, but why you use these stupid wheels for a machine with milling capabilities and such a high price tag. The linear rails (12-15mm HIWIN MGN rails ) are so cheap now, so I would not bother using these wheels. Also the rack and pinion system…I am not a fan for it, its can be fine for milling and laser engraving, but for 3D printing it can only handle slow accelerations and this will greatly affect printing times also they can be quite noisy, and will have a backlash over time.
I would replace with a strong belt system, 10-12mm wide steel reinforced GT2 belts (T belts are not really designed for a sync. motion).
Also an enclosure is a must for this machine as milling operation will make a lot of dust or chips (dust will stick to the wheels and into the rack and pinion so another minus for this solution). The laser engraving is also a very smelly/smokey operation ( basically its burning away the material) so you need a good ventilated enclosure, witch will also prevent the laser beam to exit from it, or you will not pass any safety certification with this machine.