As you're training for your PPL, check with the flying school. They can have special deals for circuit training. You would have to pay your instructor for travelling to another airfield. They may be unwilling to train circuits at your desired airfield.
If your looking for the cheapest before starting, the cheapest PPL will be the minimum hours one. Not necessarily the lowest cost per hour.
Consider Aberdeen, Perth, Inverness. What's available at Longside and Insch at present? A 3-axis microlight licence might suit you.
Aberdeen runway is much longer than Longside, which has no ATC/ATIS most of the time.