I assume that you are talking about the KB Home Townhomes in Sunnyvale that are selling from $625,000 to $660,000. The best way to go about this is to talk to a local real estate agent who can tell you what the other properties sold for. On new developments like this there is sometimes not much negotiating room left but it is advisable to have your own REALTOR who looks out for your best interest. As it would be a buyers agent it will cost you nothing. You will get the service for free!
The best way to approach this is to have all the necessary documents ready (credit check, bank pre-approval) before you get started. Make sure that you do not have too many credit checks done. This makes the banks nervous (they might think that you are actually purchasing several large items). Also it is advisable to talk to a loan broker who has a lot more options of finding the right loan for you rather than only speaking to a loan officer at one bank. If you need referrals for loan brokers please contact me.
Good luck to you.