I bought my Guide to Humanoids cheap off of ebay for $5.36 shipped. You could also buy basically anything from dndclassics for $5 or $10 or less when it's on sale. E.g, I got everything Planescape, including the 2e PHB and DMG, for $15 a few months ago.
There is no reason for me to go look for that stuff. I played 2e like twice; i have no desire or care about 2e through 4e with no experience on history or attachment etc. All my time playing this game was D&D and 1e before 5e so if I am looking for old content I am looking for really really old stuff. I have no understanding of any of the D&D realms other than Dragon Lance and that was because I read the books way back in the day. I read while over 300 fantasy books I think the only series I have read from the D&D world are Dragon Lance, Drizzt and Highwayman.
I really have no idea what Ebrron, Dark Sun and many other things people talk about when people start talking about it I just shrug and move on in the old days we did all custom campaigns and I still do custom campaigns. Hence so far I like what 5e is doing and will continue to buy 5e stuff fits into what we are playing