Airline prices (or how to make a convoluted system not even operators can understand)

A few months ago I bought a plane ticket and I needed only one way; however, it was cheaper (in absolute terms, not relative or anything fancy) if I bought a return ticket.
As if that weren't enough nonsense, now I had an extra leg I am not going to use, so I'd like to change it to some date when I can effectively use it. After listening to music for 30 minutes the phone operator tells me that changing the date, since it exceeds the maximum stay, is more expensive than buying a one way ticket (and I guess much more than a return).
I think Google will never make a search engine for plane rates. Indexing the web: easy.
Finding the cheapest rate from A to B: hard (heck, I guess it is NP-complete)