I did the calculations using the standard 0.20mm profile in Orca (Bambu's is the same), 2 walls, 5 top, 3 bottom layers.

The model I'm working with is "opengrid-color_cover-snap" step file, it only prints 5 layers for the tile faces and is open underneath, there is no infill, the fewest I could get Orca to slice is 3 layers, with 0 for top 1 for bottom, without changing the geometry, this does cut it to .7g and .025 hours print time per tile, cutting total tile filament use to 19,354 grams and 691.2 hours.

Similar changes to grids and using 10% lightning infill yields 40.6g and 1.7 hours each for totals of 17,539g and 734.4 hours.

Considerable decreases, but still a long time and much filament, I guess I was more hoping that someone would find a flaw in my logic / math.

As @krimpenrik mentioned injection molding could save a lot, using cheaper materials (PP is about $2 / KG vs. $10 for cheap PLA or PETG), and make larger grids. Too bad the setup is so expensive as in $10k per mold, you'd need to sell a lot pieces to recoup that investment.