Did some ask about Bikes?
Let me say this first. I am a serious cyclist so I can inundate you with "stuff". That being said:
1. Get to a GOOD bike shop! Stay away from Kmart, Walmart and any of these low price department store models. If you think that cycleing can be a form of exercise that you might stick with, it is important that you get good advise on what is out there now. So many advances in bike equipment have been made that you might be suprised.
2. Get something that is a bit "better" then you think you need. Why? It is an exercise format that does benefit from good equipment. If you have good equipment, you will like it better, have a better chance of success for the long term, and all that other stuff. Good bikes go faster then bad bikes, "gooder" bikes go even faster yet. LOL
3. Don't be afraid to dream about where a bike can take you. I have 4 bikes. 2 race, 1 mountain, 1 cross country tourer. Now, you don't need to go THAT insane but keep in mind that no bike does everything well.
4. SERIOUSLY investigate all the gadgets and accessories that a good bike shop can offer. Rideing shorts, gloves, helmets, fancy bike peddles that you clip to your fancy bike shoes (LOL), and such all have a place. Yes, they can add up to a bit of sticker shock at first but in the LONG RUN, they will enhance your rideing pleasure which, in turn, should help you stick with it.
5. Find a bike club in your area to learn as much about cycleing as you can so that you can enjoy it sooner. There is a bit of homework I recommend beginners do. It is critical that you learn good riding habits and how to PROPERLY shift that darn thing to get the most pleasure. Call it a little "Riders Ed."
OK, How much cash? Well, to be honest, you don't need to own $6,000 of bikes like I do. However, I would tell you to consider investing a minimum of about $500 in a new bike and ESSENTIAL accessories. I priced out a new bike for my wife and the necessities and it came up to about $750 and it was a great starter mountain bike. Why so much when you can go to Kmart and get a $90 huffy? Quality, weight, equipment. For $90 you get a boat load of garbage and frustration if you want to have some real fun and these bikes are often put together by untrained kids who will reverse cables, install shifters up-side-down, and every other back yard mechanic error you can imagine. DON'T DO IT! If you do, it will also wind up getting dusty in the garage.
Bottom line, riding a bike is not hard. Getting total enjoyment takes time, practice, effort, and good equipment. It is a bit of a gamble to do it right the first time if spending a few hundred dollars is a major issue. But, if you want to make cycleing a life-long exercise and use it to take you to the next step in fitness, then it is a good gamble to take.