Still an awesome idea. I tell you what - Data Validation is pretty much the coolest thing ever. Makes these kinds of things so good. I remember making a damage calculator for PSZero back in the day on Google Sheets using this kind of stuff.
Suggestion - should you add an "Amt (optional)" column, for things such as grinders/materials/Photon Drops/Photon Crystals?
Speaking of validation, something glitched and only about half the drop list got copied over. It's now the full drop list, so there should be a lot less "invalid" data. Probably should add in the non-dropped items as well, though I'd have to compile those manually.
As far as the quantity column goes, thanks for reminding me. It was in my head, but never made it to the sheet. Easy enough to add.
Data filters will be built up as the requisite information to actually filter begins to exist. Right now it allows sorting by GAF name and Items wanted and Items giving and items trading. More advanced queries will be eventually be possible, but I'm still working out in my head how to best do it.
The drop database doesn't have details of what a drop is, so being able to query something like "all guns with over 30% dark being offered" is rather impossible as it stands. This is compounded by the fact that the validation list itself can be overridden. As of right now, I'd only be able to offer a "all items with over 30% dark being offered" query and leave it to the user to figure out what they can actually use. I suppose I could add in a manual field for the user to specify what generic type the item is when they list it. The fun of working with a partial data set.
Edit: Added the quantity column and added a weapon type column. Both optional. (Though lets be honest here - I can't force anybody to enter anything, so effectively everything is optional. =P)