It ain't cheap...the biggest cost will be labor. With the luck you've had with your dealer, I'm not sure I'd let them do it, unless it was free because they f'd it up in the first place. It's hard for me to understand how someone cross threads a drain plug, but I know it happens, even on cars that are taken to some of the "quick change" places. That's because they have jack leg, untrained, inept people doing the fluid changes. Any idiot can tell when the plug is not threading properly during installation, but I guess they just don't give a chit, or are using an impact wrench and can't tell.
If you don't want to fight with your dealer (which I would, but that's me), I'd try to find someone on here who has swapped their inner for a chrome, as Boatman suggested, buy the part, and find an independent shop that you can trust to install the new inner, if you can't do it yourself. How the hell would HD know? If they are telling you that you MUST use Syn 3 in all holes, then you're already screwed unless you do the work somewhere else and put Syn 3 back in the holes.