I just got a Surface Pro 2 (the i5 8gb 256gb one), I couldn't afford the companion/cintiq prices. It doesn't have the wacom side buttons or pen tilt/rotation, but it's otherwise wacom tech, been very happy with it so far, for somethign that's less than half the price of the equivalent companion/cintiq.
keep in mind though that there are surfaces and surface pros. don't bother with the non-pros, they're just ordinary tablets that don't run windows.
You could also consider one of the huion's as cintiq alternatives
http://www.huion-tablet.com/product/Again, no buttons or pen tilt, but at those prices, I've heard they're pretty alright (for the price)! the bigger one especially. when in doubt, youtube reviews are a good idea. overall consensus is the lack of buttons sucks a bit, and driver compatibility/pressure can sometimes be finnicky, and the screen of the cheaper model isn't great at extreme angles. but consider that they're sub $1000 poor-man's cintiqs!