Premium credits start at $1 each and get cheaper when you buy them in bulk. On average, most users pay ~$0.80 per credit (eg, $80 for 100 credits).
Curators cost between 1 and 5 credits each, depending on a number of requirements. The simplest way to think about it is: the more impactful a curator is, the higher they can put their price.
You'll be able to see the price of each curator before you choose to send to them. In general, we recommend targeting 5 - 10 curators for your first submission. Depending on the results, you can then decide whether it makes sense to invest more credits, adjust genres, or change directions entirely (eg, using Meta Ads or trying a different single).