Yes, the prices are a bit steep but North Down is expensive, Bangor is a coastal resort, close to Belfast, etc.
PRONI has Valuation books which follow Griffith's Valuation until c1920s. However, they would not photocopy as the system of changes is based on different (now very faded) colours of ink over the years.
Working back through directories might help a bit to narrow down the date but not easy unless you can get to the libraries here probably.