Spotify's self-serve advertising platform has been in beta since last year. Right now, Spotify charges around $0.015-$0.025 per ad served, with a minimum of $250 in ad budget. The price depends on your targeting selection.Apr 2, 2018
There's more info here:
Web 'n Retail's cost to create, administer, report whats working and whats not and tweak as needed during the campaign plus detailed overview of audience and numbers on your report would be $150 regardless of what size budget you run. With the amount of time we put into ads, we're not making any money on this based on our hourly rate.
I believe you can record the voice over for the commercial, or have them do it and no further cost.