I've been looking into 6x17 cameras as well. The Malefic seems to be a very affordable point of entry, but I have no direct experience with it. If you have access to a 3D printer and some skills, you might be able to make something similar. I'd guess these types of cameras have some significant limitations compared to more refined (and expensive) options, so it's probably worth considering what you need and what flexibility you require:
- Accurate focusing / grad filters - e.g. Linhof, Da Yi, or bellows cameras have ground glass to aid, others like the Fuji cameras may simply be more accurate with scales than Malefic
- Movements - some have Rise/Fall (mainly important for architecture), bellows cameras also have tilt/swing
- Lens selection - Malefic has a pretty limited range, other cone systems have wider ranges, bellows cameras accept the widest range
- Usability/ruggedness - changing film in the field may be more difficult with some options
One of the most affordable and flexible options I've come across is a 4x5 camera with a Da Yi 6x17 back and ground glass. Basically has most of the above benefits, and you'll be able to shoot 4x5 also.
I'd be really curious to hear more about the Malefic option though.