The unspoken point in Musk's comment is that SpaceX doesn't actually care if they get these particular rockets back. They want to prove reusability, of course, but no matter the outcome they never plan to re-fly these cores. They will focus on the not-yet-flown Block 5 cores, and standardize on that going forward.
In this flight, the side boosters and center core were Blocks 3 and 4. So SpaceX definitely wants to recover the boosters, to perfect reusability, but they never intend to re-fly any of these boosters, so better to get back the one with the expensive and reusable titanium grid fins.
I boggle a little at what I read there, such as "With Block 3i, 89 percent of code required for full warfighting capability is flying". That's 89%? Not 88% or 90%?
You can be sure the specs for something like the F35 run into the hundreds of thousands of pages. Tagging exactly 89% of the features as making that milestone is probably the easiest part of the work.
They measure 4 by 5 feet, so we can estimate they are probably made from a solid chunk of titanium that was at least 20 cubic feet or almost 5,000 pounds. That would be nearly $150,000 in raw material and probably another 5x that in processing (guesstimating cost per cubic inch of titanium removal).
Either that or they were specially made castings, which are similarly expensive in low volume, if not more.
Wouldn't you be able to recover most of the removed titanium, amortizing the majority of that guesstimated materials cost? Processing likely remains expensive, however.
Printed metal has huge issues with heat, and they just switched from aluminum gridfins to titanium because of the heat. I seriously doubt that they’re usung additive techniques here.
You are also dealing with low volume fabrication which means setup and tooling costs don't amortize across many components. I wouldn't be surprised if they cost $1M each.
In this flight, the side boosters and center core were Blocks 3 and 4. So SpaceX definitely wants to recover the boosters, to perfect reusability, but they never intend to re-fly any of these boosters, so better to get back the one with the expensive and reusable titanium grid fins.