Join Date: Dec 2010
Location: southern Arizona
Some of it depends on the horse you are riding. Some horses have the tolerance to get the job done with a beginner. A horse like that can teach you basic riding, but lessons can open up a lot of possibilities you aren't likely to figure out on your own.
Some horses (and I own one) crave a rider who is always in control and providing consistent guidance. A horse like that will teach you bad habits of defensive riding that are hard to overcome later - speaking from experience.
If you don't have much money, I'd try riding on your own for a bit, and maybe twice a year splurging on a month of weekly lessons. There is a lot, such as balance, that only comes with time and experience, but a good instructor can teach you way more than $120 worth of stuff (4 private lessons where I'm at) every 6 months - and give you things to work on for the next 6 months.