Scott mentioned. 1 pass of 1 spot color is cheaper than 4 passes crom a cmyk print.
1) If the main subject is to use the logo on a letterhead, some business cards, yeap, you print it using 1 ink, 1 spot color.
2) But if your logo is normally used in a full color photographic catalog, a spot color means an aditional spot color, than mean 1 extra pass. Depending on the provider, this can mean an aditional process (1 pass on a diferent machine for example) So you define it as a CMYK combination and in this case it is "cheaper than a spot color".
3) A pantone color is prepared out of a combination of some base colors. A print house can have a stock of theese base colors and prepare some amount of ink for the specific job.
But some houses do not prepare it but send the request to a provider. If the minimal amount of ink to be prepared is lets say 5 kilos, this case could not be cheaper if you only need a small amount.
There are a lot "If s" to define if a pantone color is more acurate than a CMYK defined color.
A pantone defined color is one of the most acurate ways to define a color... With some "exceptions".
1) The color you need does not exist on a pantone catalog.
2) The people preparing the ink is using some low quality base colors. They probably will have a high quality ink for the regular CMYK projects. But thoose inks that almost no one uses...
3) Preparing a small ammount of ink. It is impressive how little ink you can use on a letterhead for example. So you only need to prepare, lets say half cup of ink for 5000 pices. So the preparation can be not as acurate as 5 kilos using scales and spectometers to mesure the proportions.
4) You are not using an ideal paper. The pantone catalogs are printed n ideal conditions. If you change thoose conditions you have some variations.
Spot color defined on a cmyk process
5) You are not printing spot colors, but cmyk process and the pantone color is out of the cmyk gammut.
6) The spot color convertion is defined in the wrong color profile.
7) Normally it is more difficult to mantain a color in CMYK process. You vary a density of 1 plate and the color turns out different.
8) If the CMYK process is well calibrated and controlled, for example with densitometers or spectrometers, the color should be ok. But there is no way to define an exact cmyk color sample if it is not printed in the exact same conditions.
I had always thought that designers specify Pantones to keep the colour standardised and accurate; but maybe I'm wrong and it's more to do with keeping the price down for a single colour.
That is the point of pantone. They are the only ones printing the catalog on controlled conditions and then they send this catalogs all arround, so the sample is the same.
In a web aplication the prices are the same if you use 100 colors and gradients than 1 color. Again is a way to standarize the color rather than pure costs.