General contracting Small Business partner trouble?

First, let me say that your partner probably isn't wrong about the premiums. At a bare minimum, you are looking at General Liability and Workers Comp. Depending on where you are located, the GL could easily be $10k+ on its own. The Workers Comp will be based on estimated payroll (including costs to uninsured subcontractors). If you are both doing work, that could easily hit $8-10k for the minimum on you as owners performing work.

Then, you have auto liability, excess/umbrella liability, property, inland marine, environmental, and so on.

When I ballpark GCs in my region, I usually say at least $20k to start...but its usually higher.

However, he should be able to provide any quotes received pretty easily, not really hard to forward an email with a quote....

Do you research https://www.google.com/search?q=what+insurance+for... and don't pay out for anything you can not see the bills and contracts for!!!

You need a new partner.