If you are on a tight budget, then why not stick with a parallel port? I run my milling machine on a surplus pc I got for free using linuxcnc. Linuxcnc is free as well. It works great too.

So let's look at what it costs just so you can use USB and Mach 3/4. A uc100 is $120, mach3 is $175. Or mach4 is $200. So you are talking about $300 so you can use Mach and a USB.

Parallel ports may be out of date, but they work just fine.