In order to calculate a campaign cost, decide on a budget or how many listeners you want to reach.
If you have a budget in mind:
Budget / CPM Cost = x 1000 listens
For example:
£3000 / £30 = 100 x 1000 listens = 100,000
If you have a total number of listeners you want to reach:
Total Listens / 1000 = Factor x CPM Cost = Total Campaign Cost
For example:
30,000 / 1000 = 30 x £30 = £900