Shipping from Canada to the States was about $30 for each package. These were packaged in as small of a box as I could make it. I re-used some Amazon boxes, putting the bulk of the cards in 600-ct card boxes then placing them side by side inside the bigger box. Any overage in cards went into team bags. Light weight packaging was used to fill empty spaces. The key is the volume of the package, smaller being better.
Coming from the States to me, both packages were much bigger than I would have made them (bigger than the ones I sent with much fewer cards). One was $50 through USPS (the large package but fewer cards) and the other was (I think) $30 using UPS. Had I packed these cards, I would have used whatever 600-ct or 800-ct box that would have fit all of them, wrapped them in a white or brown paper, and sent it along that way. I ship any trade of 300+ cards in this way using whatever box fits all the cards. This keeps the volume down and therefore minimizes the cost. I have shipped many of these larger trades in this way and the cards arrive in the condition I sent them in (as far as I know and I am sure I would know if they had arrived crushed). Another one of 750 cards is going out today for $25 in a 800-ct box.
I recently bought a small scale and have the brackets for weight printed out for Canada Post shipping costs. I also now do all my own shipping online using my small business account which saves me a couple of $ every time I ship. In a recent trade sent yesterday, I was able to keep the package at exactly 200g; had it been a gram more in weight, it would have doubled my cost. The guys at the post office were amazed that it was exactly 200 grams.
I would recommend to all to learn how to do your own shipping. Keeping the zealous Post Office clerks out of the process is well worth the time for the dollars saved. (They are not all zealous; you just don't know if the one you will encounter is or not till it is too late.) By filling in the details on their website, you get the lowest cost option in accordance with their regulations, not some clerk's interpretation of the rules.
Bruno
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Check my Profile page to see my 2023 Goals and my Lists of sets near completion (5 cards or less) or sets getting close (less than 100 cards missing and 75% complete).
https://www.tcdb.com/Forum.cfm/Page/B/ID/0/?MODE=VIEW&ThreadID=25745&C=0