There is no average campaign cost as campaigns are tailored to meet the client’s needs.
If a client says ‘we need to make some serious noise about an upcoming release, we want to reach 30,000 of your listeners”, then we would likely suggest a host-read pre-roll campaign that would cost £900:
30000 (total listens) / 1000 (CPM factor) = 30 (groups of 1000 listens)
30 (groups of 1000 listens) x £30 (cost of host-read pre-roll) = £900
Alternatively, a client may say “we have a budget of £300, what can you provide for that?”, in which case we might suggest a pre-recorded mid-roll, providing 17,500 listens:
£300 (campaign budget) / £17.50 (cost of pre-recorded mid-roll) = 17.5 (groups of 1000 listens) = 17,500
So it’s entirely up to you whether budget or reach are the primary driving factors for your campaign.