If I were to use an example of Woodleigh residences currently priced at 2.4k PSF, the nearby HDB is priced about 1.2k PSF or slightly lower which is 50% of condo sqft price, those darn sellers are crazy. Lease is similar for both.
Looking at tanjong rhu, this condo unit has 80 years lease left going for 1.9k PSF. HDB bto currently priced at $695 PSF using midpoint of $673k at 970sqft. I won't even look into the recently transacted price for HDB . Going by 50% discount of 1.9k PSF and I'm deliberately comparing it with condo 80 year lease to be conservative (with <79 year lease right), the HDB in resale will be estimated $945K. For a HDB resale at 90 year lease, it will definitely be higher, not even taking into account price inflation down the road.
https://www.propertyguru.com.sg/listing/for-sale-water-place-25183136