Thanks all, some interesting input. I have tried to gather available information from the respective websites, which I'd summarise as follows:
Motobilt
I can't see where the brackets get included, but think they are in there somewhere. Looking at their aluminium inner fender, steel outer fender and rear double arch steel flare I make the cost $1,337 and the total weight 156lbs. Motobilt quote that the front fenders give an additional 3" above the tyre and 2 3/4" behind the tyre.
Nemesis
The inner, outer and brackets for the front can be bought as a single kit (no idea why it costs more for a 2002 and earlier versus a 2003-2006), then a 4 1/2" flare can be added for the front and a 4 1/2" rear flare. The total cost for all these items is $1,967 with a total weight of 100lbs. Nemesis quote that the front fenders give an additional 4" above the tyre and 5" behind the tyre.
GenRight
The inner fender, outer fender, brackets and rear flare in 4" configuration would cost $2,050. As far as I can see they only quote a weight for the front outer fenders at 8lbs each, assuming the rears weigh about the same, and that the inners and brackets are a similar weight to both Motobilt and Nemesis gives an approximation of overall weight of 60lbs. Nothing I can see on additional clearances.
Interesting that the GenRight system may be that much lighter than the Nemesis. Nemesis quotes 10lbs for each of the fenders and the additional flares, so more than double the Genright. The rears are also quoted at 30lbs. Maybe they are using thicker aluminium as it does not look like they use a tube section.
If these weights are all broadly right, the shipping saving versus Motobilt of the Nemesis would be about $120. The GenRight option would give a further shipping saving of around $200. Adjusting for shipping would make the GenRights come in at an overall lower price than the Nemesis. But that is all based on an assumed weight which I need to check.
Given the comment above about some GenRight users being unhappy with bending at the welds, the separate replaceable flare from Nemesis may be a benefit.
The other question I have for all these options is about the replacement brackets. Where they are quoted as being handed I need to understand how they would work for a RHD where the battery is on the opposite side to a LHD.