There are several tools that can make the cost import work. However, we tried many of them, and these work the best for us.

Google Apps script to download cost data to Google Sheets. Costs from $30 per year ($2.50 monthly) depending on how many channels you have.

Bluehost to host an SFTP server. Costs around $33 per year ($2.75 monthly)

Keboola to upload files to the SFTP server. Their free tier will be enough for this.

Wrap up:

So you will have a fully working cost import tool for GA4 with your own SFTP server for around $5-6 per month. Quite good compared to Supermetrics or similar tools 😎