It's not the cheapest I know (48.04 from Dabs) click here I got the set with my new Evesham PC in December. Not had to change batteries yet, must be wearing out by now though! Just like using a wired keyboard and mouse, there's no delay. Unlike some other makes which I have tried, you don't have to "wake them up" by moving the mouse or hitting a key.
They seem to work anywhere in the same room (I do have a very small study!) so if you can see the screen, it should work.
Hope this helps.