Try installing, and licensing MC12. Once your MC 12 license is installed, try the Buy option from within MC14 again. If there's an upgrade discount moving from 12 to 14, then you should now see the discounted price.
If you already have a licensed v12 installed, then either there's no upgrade path available, or you are having other issues, in which case, it's over to the good folks at JRiver....
-marko.