Okay, no idea then - although a medium is £2.60 I think so probably not much better or worse than the place in the station! In fact not sure that they do 'large'.
Depending on what direction your coming from go to Taylor Street on the way up from Queens Road, or if your not coming along Queens Road there is a Small Batch wagon directly outside the station which is far better than the coffee served up by Flying Coffee Bean.
Taylor Street on Queens Road is my favourite by far but Small Batch is also good, as well as Red Roaster and Cafe@33.
Brighton has an abundance of great coffee shops, doing yourself a massive diservice by going to Costa/Starbucks etc.