Unlike the 24'', the U2711 does not have the rotation ability:

yes, I can buy (expensive) 3rd party arm/mount, but ...

(1) ... I would like to know if it is possible to buy such a stand directly from Dell (is the stand for the 24'' version also VESA 100x100 stand)?

The cheapest mount I found so far is this DoubleSight%20for%20$100" rel="nofollow noopener noreferrer">"Single Stand VESA 100x100" by DoubleSight for $100 [amazon.com]. 

(2) Will this (relatively) cheap stand be good enough?

Any advice on how to make U2711 rotate by 90° are extremely welcome.