Tractor Boy
You make the mistake of thinking the price for a well sorted ready to work C152 is what you see in the in the classified adverts in the aviation press, the good ones chance hands for a great deal more.
The £17K Cessna 152 will not be ready to earn any money and will require £15-19K to get the aircraft up to a standard to work for a living......... And this is at before SID's prices.
The SID's give a total airframe life of 30,000 hours for the C152 with most of the UK fleet in currently in the 9-14,000 hour range the £42-45K price reflects an airframe that will outlast most of the current crop of Rotax powered aircraft at half the price.