Yeah, paying people to scan your photos doesn't yield good results. I did that early on and found it expensive and low quality. Honestly, the process they use doesn't scale well, and I think they offer film scans to be nice, rather than because it's a viable business.

With my home setup, I can easily do 50-80 megapixels on a 4x5 negative. I use a flatbed photo scanner (the Epson V800) and wet-mount the film. It is Quite The Process involving a lot of parts (liquids, optical film to place on top of the mount, careful calibration of the focus point, etc.) but the results are excellent and relatively repeatable. But, all in, I'd estimate that it's probably a half hour of labor per photo, so you can see why labs charge so much. (Dry mounting doesn't save that much time, because of the amount of time you spend avoiding dust and optical artifacts intrinsic in using two extra sheets of glass.)

The real professionals use drum scanners. They are quite expensive, but offer incredibly high resolution and decent throughput for the operator. Looking around at prices, for $100 you can get a 320MP scan of a 4x5 negative yielding a 1.7GB file. http://www.drumscanning.com/rates.html For fine grained black and white films, you can certainly extract information that actually exists. As someone who mostly uses T-Max 400, though, that would be overkill. I can't imagine getting much more information out of my photos than I get with a flatbed.

In summary, you can see why even pixel peepers are content with their Sony A7R. Press button, get 50 megapixels. And no toxic chemicals being absorbed through your skin.