No running shoe will last for years but many will last a season or two dependent on the frequency of use. Some running shoes are more durable than other but just depends on use.
In the long run you are better off buying the name brand shoes. They last longer and are made out of better materials. The generic brands ware faster and tear easily.
Adidas running shoes have various prices. You can find some Adidas running shoes for as low as $65.00 and as high as over $100.00. Men's and Women's shoes tend to run at about the same pricing.
Yes, ADIDAS sells their running shoes online. You can visit the company's site directly, or various stores such as Journey's and Finishline to look for better deals.
Just put them in the washing machine, (cold water and just a little detergent) sans laces. If youre really anal about it, put the laces in a sock and knot the end to wash them too. DO NOT put them in...