Why don't you try DIY rebuild yourself and see what happens?
It sounds like you're interested in the whole process, and you learn a LOT from doing it yourself.
As a fall-back, you can always go BNR if the DIY fails?
$300 is cheap, considering that $100 is going to the rebuild kit itself.
Even a cheapie CHRA is going to be at least $100, so the last $100 is BNR's labor?
That's a great deal...
As for sourcing of parts...
I would worry a little about China, but I would not be surprised...
My Garrett GT-R ball-bearing series turbos all had stickers: "MADE IN MEXICO".
I was kinda pissed my ~$1,500 turbos were MADE IN MEXICO, but what can you do, right?
I know there's a lot of turbo parts coming out of South America (Brazil?) also.
As a side, I think Brembo also has a factory for in South America?
Although not BRAND NEW, there are lots of used HT-18's out there.
It might cost you maybe $100 for one, but the RA's should be in good shape, or at least be minimum rebuildable.
-Ted