I would say if you can't pay for 6-8 lessons a month you are at risk of wasting money having to cover material multiple times. At current rates of about $100 an hour for an airplane and $35 for an instructor, you need about $1500 a month. Flight training is not cheap, and you are smart for planning it ahead of time. If you can't afford 6-8 lessons a month, you may wish to put it off until you can.