Shipping Chicago to Krakow - Insurance = Taxes??

So I'm trying to ship some heavy things by sea from Chicago to Krakow. First, I was told Polamer is the best company to do this – if anyone has any insight on this company or better ones, I'd much appreciate it.

Second, every time I ship something here, even small things, I get hit with a huge tax before I can collect my item. I figured I would mark this box as not being worth very much, but stuff still seems to get lost in the mail all the time...so I want to insure it up to the cost of replacement, which is less than its current value [pretty unique, used, personal items]. If I insure it for let's say $500, does that mean that my customs declaration has to be for a $500 value? Is there any way I can insure it for more than I claim on the customs form? Will Polamer help me with this?

Thanks a lot everyone!

Insurance is between shipping company and you and the insurance company so customs does not see it (unless you tell them about it).
How much cargo do you have? dims? weight? We can help you to ship it. Pls contact me if you can.