If it is a short HDMI cable get the cheapest one, if you need a longer one (like >3m) get one a bit more expensive.
It is a digital cable so it either works or not.
Yep, 40 quid is in the "little bit expensive" catagory IMO which is just what I said, if you only need 1m a 5 quid cable is good enough.I've used a 20meter £40 cable and it worked perfectly.
