I basically ended up with using both MF as well as high-end DSLR. The MF I use for catalogue, packshots, still-life and most commercial work. The DSLR for everything I cannot use the MF.
Cost of MF is much higher than just double. Because I use it for work I figured I needed backup (2 backs, 2 bodies, etc..). Though MF backs are really reliable I still find they are somehow more vulnerable than a good DSLR. Backs kind of have an attitude, treat them well and they reward you, be careless and the results are below average.
I am addicted to the quality that comes out of the backs, color, detail, sharpness, etc.. Some clients can see this as well and some don't. I don't particularly care, I can see it and I enjoy using MF.
I would never consider MF as a replacement for DSLR or vice versa, the way of working and the results are too different.
Considering costs of a 22MP unit, that is very depending on how you are going to use it. If you can stay at 100ISO always the ZD is a very affordable option. All 22MP backs of all brands have things going for them, results from all can be outstanding. They can be bought for around 10K currently (second-hand) but I haven't been checking prices lately so maybe it is even less now.
Bodies and lenses vary greatly. Mamiya being the cheapest and widely available, Hasselblad H being the most expensive (not taking into consideration the new Hy6/Afi). Contax is somewhere in between. This is thinking about SLR style equipment.
I have also seen kits like the H3D22/39 come by as cheap as 13-15K (body/back/80mm). Maybe it is save to say you can get it for anything in between of 6K (Mamiya ZD) to above 15K.