It would be tough to find a used aluminum road bike here for under $200. By the time aluminum became a common frame material road bikes declined in popularity and there just aren't as many around as old steel ones. Occasionally you'll find an old Cannondale but those were pretty harsh riding and they'll still often go for over $200 unless they're in bad shape. I think a lot of Aluminum's reputation for a buzzy ride came from those original Cannondales.