Mach4 will cost you $200USD, do you really think that it makes sense to but the cheapest possible controller
Yes... This makes a LOT of sense to find a cheap controller. Otherwise only people with large applications who can afford to change out all their hardware will move to Mach4, and no one else will even try it. There is no legacy support for it, and while there's not a lot else I found in the same space, there are up-and-coming applications that are moving into this area, along with dedicated hardware.
And it's not $200 for Mach4. It's $2000... That's what Mach4 costs. $200 is for the Hobby Edition, and very few hobby-use-only people who need a CNC machine are going to pay thousands of dollars for one even with the hobby edition.
At a time where most people's use of CNC machines should cost around $400 all up, Mach4 risks making itself irrelevant instead of the defacto standard.
Mach3 was designed to work with a parallel port and drive everything directly. It can be improved to USB for $25 or less and work with Windows 10. Is a $400 investment in hardware really going to make much of a difference in the output of my work? Mach3 and a breakout board cost less than $200 together. Low-end stepper controllers work OK for less than $10 each.
Anyway, I'm not too worried. If there's a market for Chinese USB or Ethernet Mach4 breakout boards, then they will appear on the market and work just as well as anything else -

And if they don't appear, then it's only a reflection on Mach4 and it's failure to penetrate the market.
David