It's entirely up to the airfield operator what charge is made. A farm strip might be anything from a 'donation' to a major field charging hundreds of pounds. Your own locality will dictate what's cost effective for you.
Most fields will charge by the landing. Resident aircraft usually get a discount. As a special offer they may include a package of circuits. Rarely if ever are charges made for genuine go arounds caused by unsafe approaches. Intentional 'Low approaches' however can attract a charge at larger fields.
In the case of major international airports there may be no landing fee at all, but a 'departure charge' depending on the speed and weight of the aircraft. Manchester was one example.
As you seem to be resident in North East Scotland your options are somewhat limited in that any transit time to the nearest small airfield might well outweigh the cost saving of staying local.