Since you mentioned it, I thought it was kind of odd how the photo system worked here. On my screen the post images or “thumbnails” are bigger than the ones in the gallery view - or whatever its called when you click on a photo.
As @SpokanePeach mentioned, you could definitely cut down on costs by down-scaling everything to something like 1920 pixels on the longest side at upload. But yeah having small thumbnails that load instead of the full images is a good idea too. I think this would mean that you would need to generate a thumbnail image for every full size image uploaded.
For .jpg (jpeg) images, the “quality” (loss) factor can be reduced and that can reduce filesize considerably. Most image processing systems have this feature. 80% or 90% quality is very viewable on computer screens.
Your post reminds me I should put up another call one of these days. The price has gone up since there is more activity, it is more like $135/month now for all the expenses. The AWS as gone up to $75/month and the Mailgun is now around $10/month.
I’ll try to post a report on how much came in last time and how much things have cost since then. My memory is we were around $2000 in the black after the previous round in May '19 above. Which means we are roughly $400 in the hole at this point since the expenses in the last 18 months are around $2400.