Obviously this depends on where you are located. Such as if you live in an expensive place in the US or Canada, then its a lot more than in other countries. Also if you are young, middle age or older.
This do really depends on where you do live considering that fiat value and lifestyle status will really be different into each places.
Some do say that 10BTC would already be enough on securing their future but for some would be asking out 100's or thousands of btc.
In my part then i would say that 700-1000 would be enough to secure my future yet i can be having a savings and tending
to built lots of investment for future passive income and leveraging.