I'm gonna go against the crowd and say get an OVEN.
Just kidding. Get a 2x72 with variable speed. It'll change your life, and with the increased production and efficiency, you can sell more knives and then build or buy your own oven. In the mean time, there's plenty of companies out there that can heat treat blades for you, and give you a better end product to boot.
As for which grinder to go with... what's your budget? There are more options available now days than ever before, and it seems like there's another company popping up with a new grinder all the time. If you want to build your own from scratch, that might save you a few dollars, though at the end of the day, it may not save you as much as you'd think. That said, there's a lot of plans out there these days.
There's also a number of "assembly required" kits that allow you to save a few bucks over one that shows up at your door and runs straight out of the box. Most of these will run you about $750 to $1500 or so, by the time you get up and running.
Step your budget up to 2 or 3k, and you've really got some options. 4 to 5k, and you can buy just about anything.