Welcome. Mine should be within your budget
MPG, mine is around 25/26 average, 20 for town. Lower tax band (£240) if it's an 06 or older (I think).
Service costs, my last one was £350 iirc, including Spark Plugs. That was a P2, next is a P1 (so cheaper).
Just make sure it has a full service history, this engines are pretty bulletproof. And go for a GT, they have the goodies.