PC World has "Zoo Tycoon 2: Ultimate Collection" for PC. It costs £19.96. The best price I've seen elsewhere is £26 at Gamestation, but that's out of stock. The next best price after that is nearly £30!!
Unfortunately, (unless you pick it up instore) delivery costs £4.95 - however even with delivery it's still the best price out there for this package by far, and the delivery charge doesn't go up if you buy multiple items. Alternatively, you can arrange to pick it up in your local store FREE OF CHARGE!!
This pack contains "Zoo Tycoon 2" and FOUR expansion packs: Endangered Species, Marine Mania, Extinct Animals and African Adventures.