As I previously mentioned, IKEA used to sell reasonably priced automatically adjustable standing desks in the IKEA Bekant series. They recently introduced a new series though, that is even more affordable. For 200 euro, you can now get a Skarsta adjustable sitting / standing desk. You can also upgrade to a slightly larger version for 30 euros more. I think this is the smaller version shown here:

What’s the catch, you may be wondering? Well the catch is that the Skarsta requires manual, eh, cranking? to adjust the position:
We have tested the desk for about two weeks now here at home, and it’s working like a charm! Bonus points for the arm workout involved ^^.
Update: For those wanting more tech details on this table (which seems to be a lot of you, judging by the comments section 😉 Cam Dore just shared this useful link to the manual in the comments. Thanks!