Looks like there is a wide range of pricing for this GP, with new grandstands listed and more to come?
http://www.singaporegp.sg/ticket.html
With it being a new track, it does make it more interesting to work out the seating! I'd suggest settling on a budget and then determine what is still available, while staying well away from grandstands that are on the straights (including start/finish as you say). I'd also suggest taking a look at the basic aerial track video that they have put up on
Youtube. A couple of sims up on Youtube as well, they may give you a rough idea of the track but probably not all that accurate.
The website is saying 82% of seats have been sold so there should still be some good options. Even the GA areas look pretty decent in a few spots.
Good luck!