Flight training takes much longer and is therefore much more expensive if you are in a "pay as you go" situation, and there is always something else to spend the money on. even flying once a week means half of each lesson is spent reminding you of what you learned last week, so figure 60+ hours to get a private.

My suggestion would be to save the pennies for a year while reading message boards and pilot magazines. When you have enough to pay for 45 hours, drop it all at once, and fly 3-4 times a week until it's done. That's the cheapest and fastest way in the long run.