The cost factor, is largely in your control.
I have to assume you are already teaching ?-- if that is the case-- then rev.techn. will serve your needs, and may be studied ( at no cost to you ) at your leisure.
Suggest , when you are nearing an exam date, to get someone to quiz you on some of the mans and ladies steps, varying their questions .. it is primarily ( at this level ) a memory test, although you will be required to show a competant level of dance .
examiners costs vary-- if you are part of a days work, will be less than employing one just for you . The exam time--- 60 to 75 mins. ( dont forget to include rhythm dancing in your practical if doing B/Room ) 65 % is usually minim. pass grade --- and by the way-- good luck !!