I could be wrong, but my understanding is that these flats are only for the elderly and the lower income singaporeans. (less than SGD $1500/mth)
They are not supposed to rent out the flat & if caught doing so, you'll have to move out & the gov can take back flat from the "owner". (most of them don't actually own the flat, they are renting it from the gov)
However, there IS a black market for renting these type of flats so I believed that everything should be fine as long as you don't open the door to the gov inspectors. (Not sure how frequent inspections are carried out tho)....
Since they are for the "poorer" people, do not expect a very "nice" environment.
Prices should be around $700/mth. (Maybe higher since the property
prices are crazy right now)
Do be careful if you are renting from someone who's renting from the gov.
Sometimes, people who has been defaulting on the rental will try to rent
out the flat so that they can run off with the deposit.
(The gov is going to confiscate the flat anyway so they have nothing to lose even if you report them)
For official policies, you can refer to the gov website.
Search for "Studio Apartment".
Hope I have been of help.
Good luck with your house hunting!