When you assess the fan, if you aren't very familiar with what one in good condition should look like then you may want to find out what the original thickness of the metal was when it was new. For that, I suggest calling the manufacturer of the sweeper you're looking at. That's the best way to find out, about that and any other original equipment specifications as well. That is one area where we don't like to give an opinion on a sweeper that has been built by another manufacturer. Surprisingly, the model year of a sweeper doesn't have much of a bearing on its price.
Condition is much more important.
There is really that much variation in the conditions. Because of that kind of variation, it is important to be careful and not tie yourself to a particular model year and a corresponding amount of dollars. One is simply not representative of the other. And always keep in mind that your total cost of a sweeper is the purchase price plus what it is going to cost you to get it into operable condition. Ideally, you should keep some money in reserve in case more extensive repairs than you estimate end up having to be done.