Some question regarding accommodations,

1. What's the average rate for renting a WHOLE unit of a HDB flat?
I seem to see fewer such ads, though admittedly I got dizzy flipping through ads after 5 minutes, but I'd expect to see at least a few. Is it not a popular option e.g. low demand or limited supply or are there other reasons?
I'm curious because I am considering moving there (or elsewhere), but I dislike sharing i.e. just renting of 1 room and sharing with others.

2. Related question, how are the areas distributed according to command of rental price e.g. where are the expensive ones, cheaper ones, and those that are in-between? Because I see some ads that says 600+ sqft apartments renting @ 6k+, but some 1200+ sqft aprt renting @ 4.5k+. Any quick guide?

Sorry, been 10 years since I visited Singapore, so have totally no idea about all this. Replies will be much appreciated