Hi
It's not as bad solution as one may think. I did install M16/1.5 screws in my 1.5x1.2m CNC mill on all axis together with threaded 32mm dia steel rod(60mm long nut) . It's been more than a year and still working fine with no problems at all (no backlash as well). Just need some oil from time to time. Brass nut would do better of course. Please see my projects so you can see that the machine performs well.
It's been more than a year since I bought them, but after a bit of research cheapest ones I found at that time were @ebay. It seems to me I saw some at Screwfix as well.