I was shocked to find out that a new carbide single line cutter now costs $100. Is there any explanation for these prices? Is there any such thing as resharpening carbide tools?

These cutters are top notch quality hardened tool steel.
http://www.steveearleproducts.com/assorted%20things.htm

Mark, Thanks for this reminder. I'd known of these but forgot they were available. I'll give them a try.

It is not difficult to sharpen certain Carbide cutting tools for small items like Chequering tools a set of Dimond needle files work well or you can now purchase a set of flat Dimond hone plates at a low cost these being very popular for woodworkers rather than oil stones, have used these for re sharpening Carbide router cutters very successfully. Though over the years I have found the larger the cutting edge it cam be rather tricky to re sharpen planer blades but not impossible to do by hand.