You are better off finding a local framing shop to custom make something for you. They don't charge too much unless you opt for fancy frame material and matting.
Yes, local framing shops can make things in any size you want, it's what they do. And usually fairly reasonable, certainly less than the cost of international shipping.
I did a larger one (maybe 30" x 20") at Michael's with a nicer frame a few years ago and it ended up being almost $300.
I'd talk to some of the mail order frame places. I've used Frame Destination, and while they don't list metric sizes they'll let you spec custom imperial sizes with no premium at 1/16" precision (e.g. 23 5/16" x 33 1/16" is a bit closer). If you call they may be able to properly do metric sizes.
While I was living abroad my mom would send me care packages and I had no idea what it was costing her to ship it. I would send her aboriginal carvings or SE Asian cooking utensils all the time and it didn't cost nearly as much.
$370 did sound particularly egregious, but I just checked UPS' online quote site[1] and got a quote of $311-394 for a 5 pound, A1 sized package from California to Paris.
In my experience in Asia, Fedex, UPS, DHL etc. provide substantial discounts to customers with accounts, but one-off quotes to the US/Europe are typically very expensive.
HK Post wants about H$350 to get a 3kg parcel from HK to France. That works out to about $45.
$370 did sound particularly egregious, but I just checked UPS' online quote site[1] and got a quote of $311-394 for a 5 pound, A1 sized package from California to Paris.
I'm not quite sure what A1 sized is (ISO A1 paper? Amazon A1?) but at 5 lbs USPS quotes between $60 and $130 to go from San Francisco to Paris. For international shipping from the US, the private companies will almost always be significantly more expensive and potentially leave you on the hook for expensive customs brokerage fees.
OTOH if you want to ship it express (Global Express Guaranteed — GXG in USPS speak) that comes out to around $265 (less if you pay online) and not all post offices will take GXG packages. $60 to $265 is the difference between a 1-3 business day expected delivery time and 6-10 business days.
When I started looking at different shipping options, UPS wanted about $107 to ship it back and FedEx was a similar price. I think I ended up using DHL which was the cheapest I could find at about $80, which still felt crazy to me.
A polish shop near me can send things to most of W. Europe for far less than the post office can.
The Ukrainian credit union near me can send cash to anyone in Ukraine pretty cheaply.
I mailed some 8x10s overseas in a rigid envelope and my friend swore up and down it would be too expensive ($30+). I think in the end it cost under $10 per envelope. Meanwhile international postcards from Germany were like 2€.
What are you talking about? I was just in Germany last year, and sent a bunch of international postcards for €0.90 each. That's the standard postcard rate for sending a postcard anywhere in the world. (It's €0.45 within Germany.)
When it arrived, it had some damage to the acrylic and I wanted to return it. Amazon Support said they would reimburse me up to $20 for shipping it back, but when I took it to UPS they wanted $370 just to ship it back.
I have no idea how shipping costs are determined. I'm sure the seller didn't pay $370 to send it to me.