A feeder puts the price up dramatically. A scanner alone will often be about half the price of one with a feeder. If the feeder is essential you will find it will, generally, be directly associated with the brand of scanner you buy - for Epson you will need an Epson feeder and so on - if it is a bolt on item; I note the Fujitsu feeder is integral.
I think that those with feeders are generally aimed at office use and the premium comes because of this.
If you are going to spend this sort of money it is probably worth buying a scanner that will give good results across a range of items - photos/documents/magazine pages/etc.
Many thanks, all. Yes, I'll do some more browsing in manufacturers' 'office' websites etc. I have an excellent Epson 3200 flatbed Photoscanner which is still giving excellent service, but it would be hopeless for the no. of folders which I want to convert.