Treadmill is one of the best workout equipments for home use as well as gyms. Generally speaking, high quality treadmills cost thousands of dollars.
However, there are still some cheaper ones that are worth the money.
If you are in the market for top rated treadmills under 1000 dollars, then you might want to check out these treadmills that receive good feedback from customers:
LifeSpan TR 1200i Folding Treadmill:
Rating: 
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Horizon Fitness T101 Treadmill:
Rating: 
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Merit Fitness 725T Treadmill:
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The best treadmill under 1000 dollars:
TR 1200i Folding Treadmill by LifeSpan (2011 Model).
The folding treadmill is good for walking as well as running.
Some detail and features:
It features a biomechanically correct deck suspension system which supports a max user weight of 300 lbs. And it also has a 20″ x 56″ spacious running belt and a 2.5 horsepower drive motor.
This treadmill has 15 levels of incline, speed ranges from 0.5 to 11 miles per hour. With the handlebar controls, it is easy and safe for you to control the incline and speed when you are adjusting.
This treadmill has a usb data port which can track your exercise progress, it assists you to save your workout data, such as distance and heart rate, to USB storage device. You then can upload all the data to your lifespan fitness club account which lets you access your detailed reports and customized exercise plan.
With the built in speakers, you can use it to connect a iPod or other mp3 players and enjoy your favorite workout songs while exercising.