Yes the law does stipulate that your car should have headlamp washers and automatic levelling with HIDs. However, not all of us with IS200s have this luxury of having factory installed Xenons like in other countries so as long as you fit the lights sensibly, I don't think there'll be a problem. When it comes to MOT time, you might have to plug the halogens back in but with HB4 bulbs, you'll be able to do both lamps in less than 30 secs!
As for cost, I bought mine in Japan for around £300 and I'm sure that loads of companies will have online shops for them. The only thing is the light from the Bosch system has a very intense white colour and not a bluish tinge that most people seem to like.
After fitting, my dealer set the beam such that it was right on the uppermost legal limit when the headlamp levelling button inside the car was on position '1'. This made a big improvement to the range the beam covers since the bulbs are so much brighter, but they are still within the limits so that they don't dazzle other drivers.
Hence I can lower the beam a fair bit if the car is loaded, or I can raise the beam if driving in very secluded areas.