Someone locally is selling a 70-210mm non-uSM f/4 lens for $100 (discontinued in 1988). I currently have an almost new (yet slow) 55-200 USM f4.5-5.6 (bought for $50 off ebay) that I could sell for $100, so I'd be virtually trading for an older, yet faster lens. The seller said it's in perfect condition, no marks, dust, or wear, and AF works perfectly. I know the 70-210 is probably around 20 years old, but it is a faster lens, with probably better glass (???), but the AF is going to be loud and a little slower. I'm broke and can't spend more than a $100 on a lens right now (and the "trade" would make it free). Any opinions?