Assessing your own needs first will help in determining what might work best for you. In general, price will be directly proportional to quality, as in all of the other machines. The stair climber can provide a good cardiovascular workout. They can either target muscular resistance or cardiovascular endurance. The larger models with wind resistance flywheels best mimic the motion of an Olympic style rowing motion and give the most benefit.
Some machines now have attachments to include the upper body muscles.
Recently rolling stands have become popular to the home user. These allow you to use your own bicycle as a stationary bike. Cross country skiing is considered as one of the best cardio vascular training activities as all major muscle groups are used, including the arms. Some come with attachments to include the arms for a varied workout. Unless you can afford the good machines, you're better off making the changes in your schedule to walk or run outdoors.