Per second, per generation, per GPU second
Per-second pricing (Pika SFX, fal MMAudio V2, ElevenLabs, Sonilo, Mirelo SFX and ModelsLab) charges for the length of audio you get back, so short one-shots are cheap. Per-generation pricing (Stable Audio 2.5, Stable Audio 3 Small SFX on fal, Segmind) charges the same for a 2-second click and a 2-minute ambience, so it favours long clips. Replicate bills the GPU time the run used, so a run’s cost depends on the hardware and the queue.
ElevenLabs publishes three descriptions of the same product: $0.12 per minute on its API pricing page, “billed per generation” in that page’s FAQ, and 40 credits per second in its docs. We list the per-minute figure because it is the one on the API price list. Run a small test batch and read the invoice before you budget a large job.