I would have thought that would vary hugely depending on how much work was involved, particularly in terms of things like rerouting plumbing and waste pipes for the loo. It's not the loo & basin themselves that cost big money, it's the labour and all the hidden stuff. Can't you get a few builders/plumbers around to do rough quotes?
The biggest thing will be whether you have access to water / soil pipe nearby. If not then you will need to get a water source and route to soil pipe or a macerator (which Piglet John will urge you against for valid reasons).