Signing up an a/c with a CAMO will cost a one off fee of c.£450 (not £2500 as suggested by "robin") dependent upon the quality of previous record keeping and a/d incorporation etc.
Well, signing up under most CAMOs involves an Annual fee of around £600 to over £1000 (mine is £792+CAA fee) for a 3 year contract. Making it £2500 or so over the 3-year period. From correspondence with most others that seems to be a fairly standard amount and arrangement.
Not sure where the 'one-off' bit comes in.
There is supposed to be the 'limited' CAMO arrangement for sub-1000kg but we haven't found anyone who will offer this or tell us how we can achieve it.