You can't get a good one for the budget, and even if you could it leaves you in the same situation as the B7 A4 (given the Exeo is a B7 A4 with a SEAT badge), albeit with a slightly newer car for the money.
There are a total of 0 Exeos under £7,000, and a whopping 9 on Autotrader between £7,000 and £8,000.