Why not use threaded rod leadscrews?

Stainless threaded rod is cheaply available in 1m (39in) lengths.
I know the V thread profile is not square, not ideal for loads, not
ideal friction wise, greater wear/backlash problems, not so
linear.......blah, blah

BUT I can save a *huge* amount of money on a 1mx1m wood router (3ft
6in x 3ft 6in). I've been quoted over £100 ($180) for a new 1 meter
leadscrew which I think is OTT.

Also is there a cost-effective source for rack and pinions? All the
large 8ftx4ft pro routers use rack and pinions.

-Paul