I have a spreadsheet with three basic columns,

Town Category Cost
Sheffield A £
Bath B £
Manchester A £
Newquay C £
Stamford D £


the category is based on size of the town and are either A, B, C or D.
each category has an equal set cost (e.g A= £100, B= £80, C= £60, D= £40)
I need to know if there is a formula to automatically fill in the cost when
I enter the category in column B? hope this makes sense!