I can't say this with 100% confidence, but I believe RC expenditure is based on the overall size of your post in terms of storage space. Thus, longer posts with more text and larger images will burn through more RC.
Also, I've given you a follow. If you decide to go ahead with posting all these images, I'd happily delegate some temporary HP to help you finish posting everything, if needed. I'll make a note to check in a couple times this next week :)
Thanks buddy! I think you're right! It cost me ~40% RC for three posts :) Thanks for the offer but all is well!