newtocycling said:I'm considering it now because I need a sport so I can get back in shape, one that's flexible enough for me to do any time of the day without worrying about someone else's schedule. Cycling seems to fit the bill.
I just got back into cycling, and I'm 49 and overweight. I did do touring in college, so I once knew something. I tried running first, liking the simplicity of minimal equipment, but my hip quickly started to hurt. Cycling is much easier on the joints, and for me at least is a good balance of cardiovascular conditioning and building muscle. And it's exciting.
What kind of bike to buy depends first on the terrain where you live. I live in the foothills of the Appalachians, and I wouldn't ride a bike here with less than 10 speeds. If you live someplace flatter and you just want to ride to the store there are cruisers with 5 speeds or none.
If you want many speeds (many new bikes have 24 or more) then the next choice is a mountain bike or a road bike. A lot of people ride mountain bikes without ever going off the road, because buying a cheap mountain bike is how you get many speeds and a fairly upright sitting position. I just bought my kids mountain bikes for that reason, and because they are really easy to understand--you turn the handgrip and the gear shifts and a number shows you what gear you are in.
The downside of a mountain bike is not only that it is heavy but also that if you are going to ride more than 5 miles or so it is a disadvantage to sit upright because all your weight lands on your rear (and the shocks of the road hit your back harder). The bent over position of a road bike isn't only to reduce wind resistance but also to take part of your weight on your hands.
If you want to do fairly serious exercise on a bike--an hour or more--and don't want to ride on trails then I would go for a road bike.
The best way to buy cheaply is to buy used. At a yard sale you could probably get a discount store bike very cheap, but they cost under $150 new and the quality is pretty poor. It might be a way to get started and then see if you want a better bike. If you want to jump in more seriously find your local bike club and see if they have a place where people advertise used bikes.