There really isn't a single
way to compare this.
First define the comparable boat. Are we comparing interior
living space or LOA
? A cat will have for more interior
room for the same length.
Second, what marina? Some don't charge extra for extra beam, particularly moorings. But a med moor marina will charge based on width not length. So it just depends. And again are we comparing two 40' slips (but one a double wide) or a 40' and a 60' slip?
Bottom jobs and the like are typically quoted by square footage, so a cat of the same length will be about 50% more. Some places charge by the foot so cats are less, others double the length for cats and will charge more.
Hard spots on jack stands are often charged by the square footage you take up... So very boat dependent.
... The same as above. Typically a cat are more expensive by either comparison (length or volume) but this isn't often a massive difference.
In other words you need to provide more information. There is no one correct answer, and a lot of it depends on how you define 'similar mono and cat'.
Personally I prefer tri's. But then I am a little nuts.