U cant have both US and US maps on the 296, only 1 at a time. You can change them with a computer. Add £150 for the terrain update and £25 for the base maps (airspace, frequencies, aerodrome info)
You will need to pay for each of those items twice, as you will need a unlock code for each terrain. (even though you already have one preloaded, but you have no idea what the unlock code is) and the same for the base maps
So its better just to buy 2 units or just fly around in the US with your base map, thats what I do, So I dont get any terrain features, I just see one color for the land and another for the sea, along with all the airspace and airfield info.
Most my US flying has been done in Florida, so there is not much terrain to actually worry about