Note that some tablets are wi fi only, which means you need to be near a wi fi router, or at a wi fi hotspot, to get to the internet.
Others are wi fi AND 3G, which means it has a phone sim in it and it can also use the phone Sim to get to the internet.
Buying one that is 3G will add a lot to the cost, but he may not need one with a 3G sim, so waste of money paying extra for that if he does not need it.
But I agree with Chuck, if he is going to use it for work then it is very risky spending £500 or more for a device that may not be right.
Also note that an iPod is a tablet, and loads of other people make tablets, like Samsung, Google and so on.
Dont get sucked into thinking if you want a tablet it has to be an iPad, there are plenty of alternatives.
In fact NEXT WEEKS Radio Times (not this weeks) has a supplement about how to choose a tablet.