Apologies if this is old news, i'm sure at least a few people have figured it out (some credit) but I doubt its common knowledge.
You can get real time pricing data into a spreadsheets, trick #1 is to use the ?sid=<your server> in the URL, and trick #2 is to use use the HTML/XML parsers in the program.
Here's a <url redacted> comparing copper vouchers gil value.
I put the server id in S1, (7 is fenrir, I don't know the rest)
Couple things to note: for the most part you can paste Columns B-O to another row and just put the cookie based url you get from your browser in column A and it should work. Although a few items for both FFXIAH and the original wiki (to get the NPC price) have 2-3 different formates so some of the table indexing might need to be adjusted slightly. Columns D, E, F, I have 2-3 slightly different formats.
FWIW i'm basically combinging the "Rewards" links in the left side of this site, but it checks the sales rate snd recommends the NPC price when appropriate.
Each row is doing multiple lookups so its kinda slow, Probably best to delete the non-interesting data (which is arguably all of it once you learn the best items to AH or NPC) Smaller sheets do perform reasonably I have a 2nd tab where I was just watching the AH for relic upgrade items/mats and it was handy to see it in one place without having to do multiple searches.
AI tools like grok/chatGPT/google search can do a decent (far from perfect) job of helping you parse the xpaths (i'm slow but I can figure it out)
IF there's any specific questions I can try and answer, otherwise if I hope its helpful,