Mydata
Have you thought about the "obvious" and scanned them as colour, and then ran a batch job in Photoshop to convert them to B&W?
PS does most image conversions better than anything else out there - especially the crud*y Nikon software.
Re flatbeds, I would buy the best A4 scanner you can find. They are so cheap now it's a struggle to find one that's too expensive. I've recently scanned all the old family pics (back to c. 1910) from photo albums to TIFFs, using an Epson 3200 but I don't think that one is current anymore. It was about £300. The result is excellent, though not as good as the original photos in the range of contrast. I don't know if there are any A4 flatbed scanners on the retail market with a contrast range matching negative film + paper.
There must be a lot of people with expensive slide scanners, with their slide collections all scanned, and with the scanners gathering dust
My 5000ED has hardly got used in over a year. I suppose I should put it on Ebay before it gets too old.