Wire wheels, engine/crash bars, sump guard and a set of alloy panniers for starters and quite easy to do. But to complete the look, you really need to beef up the appearance of the fuel tank and enlarge the screen.
Have the alluminium rear tank panels powder coated black.
Add "R1200" tank stickers from Humvee Graphics
Add the black beak extension piece.
Add winglets.
A little more expensive ...
As mentioned swap to a GSA screen - you need the screen and the support bar. Expensive items but if you keep a look out they can be picked up second hand - it cost me £40 for both and a few quid for some bolts and grommets from the dealer.
Consider upper and lower crash bars - SW Motech do them for the '04 model, think Wunderlich do but it's something I need to check.
And then ultimately as Roymondo says you'll need spoked wheels to complete the "look".
Wheels are, I'm afraid, out of budget But I have seen some Hepco and Becker engine/tank protectors for 360 euro delivered to France from a German ebay site they look good but don't know what is the best to get? Got a beak coming sometime next week for the front mguard.