Overall, a bungalow costs way less than a masionette though I would not be so bold as to say 67% of the cost of a masionnete because the cost of finishes has the biggest impact on the cost of a house rather than plinth area or structural design/complexity of a house. But overall, bungalow is way cheaper to construct.
if the space is exactly the same. I.e. 3bedroom maisonette vs 3Bedroom bungalow. All rooms exactly same area... there is no much difference in costs.. perhaps costs of reinforcement bars and scaffolding for laying the upper floor slab and the staircase which generally get discounted by the reduced size of the roof cover.
Ultimately you also gain better use of your plot as you have more land for landscaping, and maybe future extensions or garage etc...
Maisonette any day over bungalow... especially if your plot is 1/8