Unfortunately, Airtable’s default values only work when a human is manually creating each record manually with their own mouse and keyboard manually.
If you’d like, you could use Airtable’s new “record template” feature to manually right-click on records and apply default values to a bunch of fields at once. But once again, that requires manual human intervention.
You could also write a script in a script extension, but again, you’d have to manually trigger the script.
So automations are the only way to go.
But as you mentioned, Airtable’s automation runs have low limits with no ability to purchase any more runs.
This is one of the reasons why I always recommend Make to everybody. It’s my favorite automation & integration platform, and you can buy as many automation runs as you’d like. You can use Make’s CSV modules to automatically parse CSV files that you drop into a cloud drive somewhere, and then you can import all of those records into Airtable with the default values that you specify.
There can be a bit of a learning curve with Make, which is why I created this basic navigation video for Make, along with providing the link to Make’s free training courses.