HDB is "run-down"?? How dare you!! I paid a BOMB for my HDB flat okay!!!
Just kidding okay.
It really depends on which estate you're looking at. The newer estates look really good on the outside - landscaping, colours, etc. Places like Tampines will appeal to you if you're looking for "modern-looking" environment.
However, don't write-off older estates as well. Often, these older estates have an advantage over the newer estates in that the amenities are more or less established. The one I'm staying at (Ang Mo Kio) has a well-established Town Centre, with sub-centres around each neighbourhood. I'm not sure if the new estates have such "nodes." Also, the estate tends to be more spacious between flats. The flats in new estates are more cramped together.
Also, MRT stations tend to be built where the housing estates are.
The govt has been and is building new flats in the old estates to replace the really run-down flats, so you may actually stay in a rather old part of Singapore and yet live in a new flat. One thing I don't like abt these new flats is the layout is really odd, but if you're only renting not buying (and subjecting yourself to a 25/30-year mortgage), I don't think it really matters.
$500 for a whole flat sounds suspicious, unless it's a really small flat, it doesn't come with furniture, appliances (like washing machine), and a functional kitchen, and it's in some really, REALLY old part of town which is not serviced by public transport.