For most products like business stationery, booklets, leaflets, posters etc full colour printing is the cheapest option. This is because the printing process is not only cheaper but also printers can ‘gang’ jobs up of a similar nature, so the presses aren’t tied up with just one job.
Spot colour printing still exists but nowadays we can convert the spot colours to full colour to bring costs down. Remember though full colour printing can only approximate a pantone colour it can’t replicate it exactly but most good designers can show you on a colour chart what the final colour will be.