So I'm getting back into photography again, I upgraded my 400D to a second-hand 50D which I love. I kept my thrifty fifty but sold the rest off as it was kit lenses from a few years ago and the body. I found (and already bought) a (new) discontinued sigma 18-200mm f3.5-6.3 as a general purpose and in the future I have my eyes on getting a nice wide angle and I would love to get a second-hand 70-200 f4L lens if one come up on "that auction site" for my budget.
My question is what is everyone's thoughts on buying cheaper older, second-hand and/or discontinued lenses. Will they compete? I am doing this as I have three kids and other expenses so I can't just drop a thousand on my hobby. I can push to three hundred or slightly more every so often but even then the choices are limited. I found a place in Sydney which has lenses for much cheaper and the reviews from four or five years ago are good but can they be viewed as relevant to today's standards? I know the L lens is not included in this except for it being second hand.