Depending on what kind of expenses are in question:

a) once-only payment - jednokratno plaćanje (also: lump sum payment)

"The licence fee is a once only payment, as the licence is issued for life. ... "

www.marine.transport.sa.gov.au/faq_answers.htm


b) non-recurring fee - jednokratna pristojba


c) non-recurring cost

Non-recurring Cost - Costs for one time efforts such as design, studies, drafting, etc. (see the site below)

Hope it works for you!