As far as i can remember, in the 80s, subsequent to the opp's query, the gahment was unable to ascertain the amount of 'real dollar' subsidized per unit. After some streamlining process, they managed to cover those patches and it appeared to be transparent

From a start, SLA sold land to HDB at a higher land price - I wonder what is the benchmark ? Benchmark from the private sector's land sale ?? SLA sold the land, made profit from it (1st tier of profit). HDB took over and developed it using market billable rate - assuming HDB Engr based cost is $30/hr... book billable rate $110/hr & bank lending rate at 6% etc (2nd Tier of profit). Hence on paper, HDB may/may not suffer book losses.
Firstly, the SLA was created only in 2001. So, in the 80s, if you recall, most of the land sales were done by the URA. As a side note, even I don't know why the SLA was created, as they have the same goals and objectives as the URA. The URA sells to private and commercial developers, while the SLA sells to stat boards, and also private. Just another whole new bureaucracy created to feed PAPpy peons at the public trough.
Anyway, if you are talking about the benchmark, than the only true benchmark that you can use is what the govt. actually paid for the land. Not what they say is the "market value" . So for example, if the URA exercises the Land Acquisition Act and buys your grandfathers durian plantation for what he paid 40 years ago, he will get maybe $100 PSM if he is lucky. URA rezones it, does the soil studies, and surveys, and sells the land by tender to a developer for $4000 PSM. The URA and SLA will now claim the market price is $4000 PSM. And this is the price that HDB claims it got its land at. We all know its bullshit, and this cow Kee Lay Cheng can't seem to understand it.The benchmark to be used is $100 PSM. U are right, this is the 1st Tier of profit.
Further profit is made by added on construction value. The sum of cost of construction including financing costs, materials, labour, architecture, etc. is only 50% or less of what they charge the peasants.
The largest profit is made by denying the peasants the ownership of the land. HDB claims to have paid market value for the land, but they are not passing ownership of the land to the flat buyer. So, in 99 years, they get the flat back for free, along with the underlying land. The prepay lease (what the buyer paid for his flat) is 100% profit to them.
Than they make more money by earning interest on the prepaid rent that you had to borrow from them. They make additional money by forcing you to take upgrades or pay for the repairs of their shoddy products. And before the 99 years is up, they wil force you to relocate to a new estate and pay even more.
Finally, Lee and Lee make their own money by doing the conveyancing for the flats.