My advice is to stick with tried and true brands...... My personal favorite is KMG/Beaumont Metal works, but Bader, Burr-King, and a few other that have been around for a while.
Just steer clear of all the johnny come lately ones! The majority of them are just trying to cash in on the currently popularity of knifemaking....and when you need them, they won't be there. If the price seems too good....there's likely a reason. There are a couple that are currently being sold on Ebay for around the $400 mark, that have gotten a lot of attention from those who don't know any better. I've seen both in person (because folks brought them to my shop, wanting me to help them "fix" it).... the only way to describe them is.... they are a SCAM.
I'm not against building your own, it's just that a good majority don't have the tools, or fabrication skills/abilities to do it correctly, and end up with just another machine they are frustrated with. Besides, unless you just want to do it yourself, by the time you factor materials/parts purchases, and your time, your at, or very near the dollar amount of buying a "good" one.