This has been covered somewhat extensively in even some recent threads, but the OregonBladeMaker chassis seems to be the best bang for the buck.
Just under $1k will potentially get you a full flat platen setup with a low cost variable speed set up. This leaves room for future tool arms (at additional cost of course) vs. just buying a 1 speed grinder like a craftsmans 2x42 or the Grizzly 2x72.
Polar Bear Forge also makes the SLING kit grinders that can be put together a little more reasonably, but don't really allow for future tool arm changes and what not.
Lastly, you could build your own for potentially less money yet, but that really depends what you have available locally, what you can scrounge up, and how good you are at building tools. In that case, something like the NWGS is a good option.