How to calculate shipping costs to avoid overpaying?

tldr Does anyone have a good website or link to reliably calculate shipping costs from china to the united states for verification of shipping expenses?

I got some cheap low weight packages I wanted to order through alibaba. The 'price per piece' is like 20 cents. For a thousand of them the package weighs 15lbs cardboard included and is roughly 16"x12"x12". So its not a massive package.

When I asked for the shipping costs the lady initially quotes 245$ for shipping. I said I dont need express or anything just whatever is cheapest. Then the price suddenly dropped to 110$ for shipping.

I cant tell if she was just trying to tack on extra shipping costs for the sake of squeezing some extra money out of me.

Doing my own research, trying to find freight forwarders and looking into some independent shipping brokers, the lowest price I could find was like 145$ if I arranged my own shipping.

But I've gotten similiar packages from other suppliers that weighed maybe 5 lbs and shipping was only 15$.

Thanks