Good thing we have reams of data on this, holding performance constant the cost goes down 10-40x per year: https://epoch.ai (like the first box)

Also, frontier token prices have remained roughly constant:

3.5 sonnet: $3/$15 3.7 sonnet: $3/$15 Opus 4: $15/$75 (opus tier) opus 4.1: same Opus 4.5: $5/$25 Opus 4.6 (same) 4.7 (same) 4.8 (Same) Fable: $10/$50

So Fable is cheaper than Opus 4 was at launch.

One thing that has increased quite significantly? Spending and adoption.