If you have a bike co-op in your area, I strongly recommend paying them a visit. First, you will meet a bunch of knowledgeable people who would be happy to help with advice. Second, co-ops may have a bunch of donated bikes that would be available for you to acquire at a very low price. Sure, they would likely need a good tune up and some minor repairs; however this is a learning opportunity. I never advise new or casual riders to spend a lot of money at first before you know that you will get good use out of them. Good bikes, like most other fitness equipment, sell for hefty discounts once the buyer tires of them. Or they end up being donated to a bike co-op.