I lived for some years in Marmount Gardens, back in the 1980s, and was therefore particularly interested to come across this advertisement in the Belfast Telegraph from 13 January 1939.
MARMOUNT GARDENS - New Semi-Detached Villas for sale. Deposit £20. 18s 9d per week including repayments, ground rent and taxes.
Thomas Henderson & Co, High Street.
Those old newspaper advertisements are a great source of information about old Belfast, in this case when the houses were built and the cost of them.