Actually there's no reasonable price for a property. When a developer sell their property,they are pricing cost+ mark up = profit. That's probably some real profit.
After that it's the market condition in sub sale market that will actually decide the value of your investment.
It may spike to a unreasonable level but it will also drop like flies.
Good example is HDB. Build in 1980s,price at 40k or 110k . But fast forward 2024, even with lesser lease the price spike to 1million sgd.
Good example is china,bought at 3 million RMB but can only sell at 1.2 million rmb in 2024 via forced auction.
So in actual fact, it's the market condition that dictates the market value of the asset.