There is, on the Manx Government internet site (www.gov.im) the email address of the Registry - I emailed them earlier this year and got an email back with a list of charges for the services and forms to complete for marriage and birth/baptism records. The fees then (March) were (quoting from their document):

D. FEES
These may be made by cheque or postal order, or if from abroad, by international money order,in UK Sterling and made payable to “THE ISLE OF MAN GOVERNMENT” and crossed.
Search fee (for each year or part year searched) £3.00
Short copy of birth or adoption register £5.00.
Copy of marriage register. £5.95
Copy of death register or burial register £5.95
Full copy of birth or adoption register or baptism copy £5.95

They may have changed in the meantime, of course!

Roger Sainsbury