That is a 'how long is a piece of string' type question.
If you have your heart set on a flat, it is worth more to you than someone else who isn't interested. To equate that to a $ value is not possible other than to see how much more you are willing to pay.
Depends on many things - 1. Do you have the extra money / finance. 2. Even if you do, would you want to spend it as you may have job concerns etc.
The list goes on.