Be precautious buying treadmills on the internet. A friend who once worked for a treadmill company once said there was some scam artist in Europe claiming to be selling their brand for considerably less. She claimed she bought them in a closeout. She was trying to get people to transfer money for non-existent products. Same situation occurred on a certain website.
Only consider refurbished treadmills if they come with an adequate warranty. Make sure the original manufacturer refurbished them. I encourage you to buy a new treadmill with full warranty coverage like the Reebok Treadmill. If your budget is limited, be diligent and get a model with a good track record and limited usage.