You will be lucky to find a full time PPL ground school however, what you need to ask is are they teaching you the things you need to know to fly an aeroplane safely, or are they just teaching you what you need to know to pass the exams. As with most education these days passing the exams is the priority rather than learning the things you need to know. If they are doing the job properly it will be money well spent.
As an examiner who conducts the PPL Skill Test and the oral exam, I am amazed at how little the average PPL candidate knows about the machine they are flying. I often find it hard to believe they have passed a written exam.