You should make a good estimate how much it is going to cost you, purchase price, insurance, maintenance, repairs, mandatory inspections, etc and whether your are OK with it. There is a good data available for most common airplanes so it makes sense to know upfront what you are getting into and be prepared. I know you are in UK but some principles of accounting remain the same - there are numerous threads on PilotsOfAmerica forums discussing exactly this topic and looking at various aircraft. As you can expect this question had been asked hundreds of times before.