Plan is definitely to injection mold at some point, but this is for several different complex parts that will be expensive to mill molds for. The breakeven point between injection molding and 3D printing is really about the cost of the molds. Let's imagine a 1kg part. If you say 10x $1000 printers at 1-2kg/day and $10-20/kg filament then you can produce 900-1800 parts in 90 days for a total of $15-30/part. Meanwhile with injection molding you have a mold cost of $5k-50k and say $3/kg for pellets, so for 1k parts it costs $8-53/part. So if you're making a thousand 1kg simple parts ($5k mold), molding will be better. Making a thousand complex parts ($50k mold), 3D printing is better. And making five complex parts (5x$50k mold), you can do a lot of 3D printing before injection molding becomes competitive.

I am also in a bit of an unusual situation because of the size of the parts: voluminous enough that shipping from the manufacturer is no longer negligible.

Oh, and unfortunately can't do resin because of strength reasons. 3D printed ABS is already pushing it.

Yeah that's tricky. I suggest Occam's razor: environmental control is likely to be the most serious factor? Any $1k printer should be able to extrude filament at the right rate in the right place, and I don't know that ABS is particularly challenging to melt. The difficulty seems to be in fume management (extraction) and the parts not warping on the bed?

Or you pay a lot of money for a higher end printer and make use of a support contract where they can figure out where your parts are failing.

One other suggestion would be to contract the parts out to a company like Shapeways and see if people are actually able to reliably make them in low volume, then try to replicate. May be a dumb question, but presumably you've tried to print the same parts in PLA or a more forgiving material to confirm that they are "printable"?

Oh, to be clear I'm not having parts fail, I was more trying to figure out ways to increase strength, along the lines of this article. Your comment is good advice if someone has a part that's tricky to print, though, good to keep in mind.