I can help calculate postage
(I believe I have a website I can post to help also) I think last year was when we had the most international (from US) participants & that was 3-4. I think each card was still less than a dollar.
If I recall correctly we have around 20 give or take 5? It really varies from year to year though
One year we did it & had 35 & another year we only had 10 or so ... so really it is unpredictable