Where can I find historical data on HDBs?

I'm planning to purchase a resale HBB. May I know where I can find historical data on the prices of a particular unit? i.e. How much was the BTO price for a flat that TOP-ed 2005, what were the transacted prices during 2010, and what are the current prices now? This is so that I can roughly gauge how the units in a particular region appreciated/depreciated over the years.