The first decision you need to make is whether to buy one with a petrol or diesel engine. You'll find a lot of diesel Octavias within your budget but these are only really suitable if you cover a lot of long, motorway journeys and travel more than 12,000 miles a year. If you do, the 1.6 TDI will provide the cheapest running costs. If you don't cover so many miles, a diesel won't be suitable for your journeys and you risk high maintenance costs. In this case, a 1.4 TSI ought to be reliable and cheap to run. Your budget will get you a 2016 model.