There are few differences between places, but the most common is you buy a certain number of birds for the day, and then it goes as Mike Harrell mentions in his post.
If it's a team from a foreign country they will need cartridges, accommodations and all kinds of transfers to and from airports, lodges ect. This will add up to the price.
Some places have a minimum of birds for the day, that it's pretty high.
It's not uncommon in Spain to have a minimum bag of 400 partridges.
Price in Spain should be around 30-40€ per bird, and more or less the same in the UK, but in pounds!
Grouse is much more.

HM