How long do speakers last?

Unabused speakers last a long-time. As has been said above, speakers with linen or butyl rubber / neoprene surrounds will last many decades. Foam surround speakers less time, but still a couple of decades.

Older speakers had issues with surrounds, but you can get them refoamed. On rare occasions, you might have the paper dry rot and then you might be screwed.

Thank you all for your replies. There is some great wisdom here. 

Considering how little I am paying for them, the worst case is I can just sell them without a loss if I don't like them. But from all accounts they should be great speakers that I will enjoy for many years.

Thanks again for the insight and replies.

I just re foamed my pair of Bose 301’s that were bought in 1977 and they still run great. I use them for my front surrounds in a second tv room. This also includes having them in a garage setting in northern Wisconsin for 16 years as well.

Insanely good  price and they sound fantastic? -- I can see why your are worried.