Hey! I can't speak to the exact mechanism for pricing on a large or enterprise level account, but it sounds like you're just getting started with tracing - might be worth checking out Lightstep. Pricing is pretty transparent for different tiers of non-enterprise usage and it's seats+services monitored, NOT consumption, so there shouldn't be any end-of-month surprises. (https://lightstep.com/pricing)
Lightstep and several other vendors use open source standards so worst case scenario, you have great instrumentation even if you're not paying for a product right away. /shrug
(full disclaimer, I work at Lightstep albeit not in sales)