Feels to me like the injection pump is the common, expensive, major component that requires replacement in reviving a hmmwv that's been in storage for a long time. I don't know if they're just the weakest link? Or maybe just the most expensive part that suffers the most from sitting without use.
It would be amazing if there were cheap new pumps out there, but those days are gone.
It takes specialized equipment and knowledge to correctly rebuild them. Anyone who has the equipment and skill to do the rebuild properly, certainly knows what the going rate for their profession is and it's not $400.
If you're buying a 'rebuilt' pump from anyone for $400, you're being misled that it was 'rebuilt' , or buying from an idiot as a truly rebuilt pump is worth 2x or 3x $400.
When I've had pumps rebuilt by a qualified shop with the proper skill/knowledge/test stand it was $800-$1100. Wasn't the best experience and I don't have anyone to recommend.
If RWH says 'I get my pumps from x' that would be my next source, no questions asked. But that probably would just drive up demand and prices, decreases availability for RWH, so I won't be holding my breath.