July-August cost was $5 USD again (which turns into $7.50 AUD, plus $0.23 exchange fee). As I seem to have gotten this reliably below the extra $12.50 USD charge I'll leave this as the last post until something changes.
As it stands the upkeep of https://popcornrequests.com is costing $5 USD per month in hosting fees (charged on the 11th of each month) and $8.57 USD per year in domain registration fees (charged on around March 8th of each year).
Thank you to the couple of people who have already helped out with keeping the web app online :)