We did our downstairs bathroom with mosaic on the floor - it's not a big room so in fact was not that expensive. We have a wet room and I think it looks nice with mosaic because you can't see the slope in the floor to the shower drain.
We got ours from here:
http://www.hgc.ch
because they have a big selection (and a kids play area in the store which made browsing so much easier!)
Basically if you want to choose the combination of colours exactly - so 40% white, 20% green, 20% pale blue, 20% darker blue (like ours

) then this costs a lot but if you choose one of their pre-made colour combinations this is a lot cheaper - both of those options came in sheets we were never given the option to have individual pieces so they made up the sheets with our chosen colours. I can imagine that a tiler would charge more to tile a wall with mosaic than a floor because it's harder.... I guess.... maybe they have some special gadget that makes it easier! I don't really know it's true just imagining how hard it'd be to put a mesh of wobbley mosaic tiles on the wall....?!
It looks gorgeous though I have to say

I would have done it for the whole room if it hadn't been so darn expensive (although perhaps may have been a bit too swimming-pool-ish!)