Nick,
The weight will be a factor, but that price does sound a bit high to me, too, tho that could be the going rate from DSL for a tube that weight and size..
I would also inquire to see what it would cost to have this tube sent via USPS international Priority mail. I think that would be a bit cheaper as I sent a tube a couple years ago to the UK, that had 3 linen backed US OS (27x41) inside, and the cost, if i remember correctly, was about $65-70.00 USD. The tube I mailed didnt have the added insurance, so that would have to be calculated in, if wanted.
It got there in about 3-5 days. And it was also mailed from the Los Angeles area.
Prices likely have gone up a bit but it might be worth looking into, especially if PM will give you the weight and length of the sealed parcel.
I would not think PM would be bothered by you asking about other, possible shipping options. In the end, they want you to be a happy customer, from start to finish.