Think the cheapest way of getting to Kazakhstan (from Europe) is with Air Baltic. Used them to fly to Uzbekistan last October (one way $ 150 from Amsterdam).

There are some cool things to do in Kazakhstan but the distances between sights are huge and I think it is mostly nature and tribes (not sure).

I went to Uzbekistan because there is lots to do (old silk route cities) and all the sights are rather close and mostly linked with a good railroads.