I just bought one of these instore. It's a good basic model that does all you really need (reads systolic, diastolic BP and pulse). It comes supplied with batteries and a travel pouch. It's clinically validated and easy to use.
It's highly rated on amazon, where it is currently selling for £17. RRP is £47, if you can believe that.
It doesn't have a memory for keeping historical readings. I suggest some form of notebook and pen ;)
edit: Cuff size is medium (22-32cm)
Changed spelling diabolic => diastolic :)