From the research I did on "normal" sharpening, I've found a bit of a range of prices, but the middle ground is something like:
$3 for blades up to 4" long.
$5 for blades 5" or over.
Most places charge an extra dollar for fixing a broken tip, or removing an over hanging bolster.
Again this is for a standard type sharpening done with power tools. A hand sharpening is a whole other thing, especially if you are trying to tailor the finish to the blade with different types of water stones, etc.
Brian.