Building a Joes could run you anywhere from $3000-$7000, depending on how you build it.
The original Hybrid has gone through many upgrades. Most people building Joes machine now are using the rack and pinion drives from CNC Router Parts.And if building a Joes, I'd highly recommend using the hardened steel V rails, rather than the base model angle iron.
For $1300 more, I'd highly recommend upgrading to the CNCRP Pro series, as it's a far better machine than the standard. But it'll come in over your budget, without software.
Imo, you can build a Joe's for less, but what you get will be relative to what you spend.
With your low budget, you're options are pretty limited, so you're in the right place.
Another option is a Mechmate.
I'd spend a few months doing research, before you spend any money.