The GrooveA combined with a 5db omni antenna would probably be the least expensive to start with, but any MT device with a Level-4 license will work.
400m is too much for a laptop though. You'll be lucky to get 40m indoors and 90m outdoors. In an outdoor network, a laptop might see an AP from 2-3km away, but it will not be able to associate. You can probably get a little more distance with a larger antenna, but not much. The laptop is still the limiting factor.
To cover a 400m radius for laptops in an outdoor environment, you're probably looking at 35-40 access points. Indoors, it's much more, depending on the layout and materials in the building, it could be as many as 150 or more.