Ben
It's important to appreciate that aircraft ownership involves both fixed costs (that you incur even if the wheels never leave the ground) and flying costs that arise out of each hour flying. Your £200/month will only cover the fixed costs (insurance/hangerage/annual check etc). The hourly costs not only include the fuel but engine replacement (say £6/hr for a C152) and maintenance (50 hour checks), say £10/hour. So you need to assume another £16/hour cost on your figures. Then there is other wear and tear costs, e.g. tyres which will take a hammering when you are doing circuits. Remember everything that is aircraft related costs much more than you would expect, even replacement light bulbs are a significant expense!