The Estate is still fairly new (first out mid 2009) if a hatch would do wait a few months until the first ones are three years old and the large company fleets are selling them off. Already early Insignias are less than £8K so they will go down a lot later this year when the market starts to get flooded with them especially for the higher mileage ones.

But: if it was my money I'd buy a Vectra as I don't really like the Insignia as much and for your money you will probably get a very tidy late estate version.