You have several options for an indoor cycling bike, from low-end, inexpensive exercise bikes to very high-end models designed specifically for cyclists. You can even invest in a cycling trainer or a set of rollers that work in conjunction with your regular bicycle to make an indoor cycling bike set up. Choosing the best indoor cycling bike is a matter of determining your cycling fitness goals, your budget, and your space constraints within the home where the bike is likely to be used. Think about how often you are realistically going to use the bike and make a determination of your needs from there.
Basic indoor cycling bike models can often be found at sporting goods stores or big box stores, and they are usually fairly inexpensive. They are also not generally the highest of quality, but for someone who will only be riding the indoor cycling bike periodically and lightly, these models work just fine. Try to find one that you find comfortable, and that has the features you want and need, such as cup holders, heart rate monitor functions, and so on. The bike should be as adjustable as possible to ensure comfort. These bikes are great for people who will ride only semi-regularly and who are not necessarily serious about the sport of cycling.
Higher-end models tend to be stripped down of electronics, though they tend to be highly adjustable for supreme comfort. These indoor cycling bike models often feature clipless pedals, or at least the ability to accommodate clipless pedals, which are specific types of pedals that work in conjunction with a cleat on the bottom of a cycling shoe. The resistance adjustment on these models is much more efficient, and the adjustability will allow you to mimic the riding position you will be in on your outdoor bike. This is a good choice for more advanced cyclists or professionals, though you should be prepared to pay significantly more for such models.
Many cyclists choose to use indoor trainers or rollers instead of an indoor cycling bike. An indoor trainer is a unit that attaches to the rear axle of the bicycle, thereby lifting the rear wheel off the ground. A metal or rubber roller presses against the rear wheel, and that roller is attached to a resistance unit. Rollers are different than trainers; these devices force the rider to keep his or her balance while riding on strategically placed cylinders, making the indoor riding process much more difficult. These options are great for more serious cyclists and for people who do not have a lot of space within the home for larger, bulkier bikes. The trainer and rollers can be folded up and stored easily after use.