1./ They are from a commercial wrecker's in Aussie dollars. For Aussie buyers the price with post is as cheaper or cheaper than many US wreckers for std or old parts pre Roadster in excellent condition.
2./ Possibly double the price of non-RocketX parts, some justified due to rarity like rear guard and side-cover with issue # for someone with an RocketX. If you just have another model and want black bits they are still probably competitive with getting other colours and repainting.
3./ The possibility of getting matching paint work for the guard at a better price in unlikely. That paint method used is unique to the RocketX with the bare steel stripe ground/buffed with unique swirls etc on every version and then a heap of clear layers. If I had an X I would probably buy it even with the slight marks it has because if some idiot every hits your rear guard you would be greatly out of pocket to find a replacement and not many work shops could ever match exactly the special paint process.
4./ Being RocketX they will be trying to bump the price to whatever they can get. They will meet the market if the items do not sell in a reasonable period. Watch them and if they haven't been snapped up you may get lucky eventually or make contact and make a multi item deal as they are likely to combine postage at a minimum.