From a purely economic point of view, it is cheaper to buy only if you fly a certain number of hours per year. In the US, this is said to be between 100-150, you should talk to owners in your area to find out what your numbers would be.
If I was in your position, I might approach some syndicate and offer to fly their plane during 'off peak times'. You might be able to negotiate a good rate, as the plane is only making money when it is flying. If it sits unused during the week it is essentially costing money.
If you do buy, it is going to cost you a lot more than you would expect. You need to talk to owners in your neck of the woods.