Sell at different prices for different quantities (e.g. 2 people at 100 GBP each, 3 people at 75 GBP each)
For tour departures / tour freesale.
To turn on quantity based pricing go to tour setup (for the tour), rates tab, turn on quantity based pricing.
You can then load prices (and supplier costs) for between 1 and 50 people on a booking (departures) or 1 and 10 (freesale). If there are more than 50 (or 10) people on a booking the 50+/10+ price will be used.
For quantity based pricing for more than 50 people then you have to use options e.g. large group discount or you could, like for tailor made tours, edit prices within a booking (once received).