I have a Nikon Super Coolscan 5000 but unfortunately this only scans 35mm negatives and positives (which is why I bought it in the first place). For medium format you will need a flatbed scanner, there are a number available. I am sure there are companies who will scan the negatives for you, but at a price. The processing lab will put them on a CD ROM for you, but from past experience (for my 35mm slides from Fuji) the resolution used is quite low.
I don't know if they still do it but some of the better Epson flatbed scanners were able to scan medium format film and slides. I used one to scan is some of my Dads slides from his old Microcord DLR and the quality was excellent with the right processing.
Why not go the whole hog though and buy an enlarger kit. YOu can pick them up for peanuts now.
I have had best results using a decent digital SLR on a tripod over a light box. A cheap enough 5x4 light box can be had for very little on the bay. If necessary, a little inventiveness will keep the negative flat. Easy, quick, and cheap.
I made my own scanner for larger format film using an old Kodak 6.1mp camera on a tripod pointing into a card box also tripod mounted, the card box with a frosted screen at the back, the neg was framed in a card slide that slid in the box in front of the frosted screen, the light was provided by placing the box pointing at a window. The camera in macro mode took very usable copies.
There you have it. The Epson Perfections do a decent job by all accounts but otherwise you are looking at s/h Nikon or Minolta for 1k+.... or scan them for proof on an Epson and chosen frames get scanned on a drum or Flextight at a lab.
Or shoot ff digital at around 24mp+ and save yourself the bother....the only way you can exceed this quality is with optical printing of mf as any scanning gives you back a digital file!!
Look for something like a s/h epson perfection 3200 on eBay........one went for £30 a few months ago. I used one for MF b+w negs a few years back and it works well....I replaced it with V700 and the image quality is close.....the V700 has other advantages however particularly when scanning 35mm film. Scanning technique and right software makes a difference.