As far as I know, you're not likely to find a standard non-CNC machine that comes with ballscrews (particularly the Chinese mills...). I would also imagine that if you did find one, it would be rather costly.
I have converted a small (Sieg X1) mill to CNC using the standard leadscrews and nuts. It has been very successful at this scale, but I have heard from many others that on the bigger machines (I would class 24 x 7 as 'bigger'), you really do need ballscrews to get the accuracy. You don't want a sloppy machine - especially a sloppy metalworking machine...
The other 'problem' with ballscrews and manual machining is that they can be a bit too efficient. There is not much resistance to stop the table moving when you are machining, whereas an acme screw won't allow much movement. With CNC this isn't a problem, as the motors provide holding torque which prevents the unwanted motion.
I have no experience with those nuts that reduce backlash, but I'd rather wait an extra few months (or years...) to save up for ballscrews, or maybe use those nuts temporarily while I sorted out ballscrews. I know they may work very well and all, but I always thought they just seemed like the 'cheap' way out (says the guy who used the standard leadscrews AND nuts... ). hahaha
Have you thought about just getting a 'standard' machine and then putting ballscrews on when you CNC it? That's what I would do.