How much is C3A deputation allowance for Europe onsite?

Also compensation depends on your India Salary, as you will get deputation allowance + India Salary. If you are earning around 1 L per month, and planning to travel with family then don't think of Savings, enjoy your time there and explore places.
If you are travelling alone, then you can save some money.

5000 euro / GBP near about per month