There's also the pricey United Exclusive (see bottom of the page) repaints of Powercore Combiner Microns. Most of them are painted in plain black/silver to resemble the original G1 Targetmaster, and were gifts with purchase in Japan if you spend 3,000 yen or more at various locations/times (making them quite hard to get a hold of). On the secondary market now, you can expect $30+ for each of them :(
And if you're after expensive repaints with weapon partners, you can't go past Million Publishing's Exclusive United Stepper and Artifire (Artifire's got two little guys that turn into weapons to justify his price) ;)
Edit: @Liege: BBTS Stepper's gone down again! :) Stock levels at 175 units. Argh, I just made a few purchases elsewhere..