I don't think most said anything as they don't like giving bad news...
I think the natural dyes and the increase of hued EM wearables really hurt the sigil market. Sigil used to be popular because the bright purple made collectors and bank sitters stand out. Now, especially with the dyes, slime cloth, specialty cloth, tokuno dyes, hued artifacts etc... folks can make outfits even more eye-catching... even things like the lanterns that held some value with collectors have been made more common by smuggler's lanterns and other event items
I'd estimate about 200-300k personally IF you can find a sigil collector or someone interested in starting. Otherwise... I'd have to say 100k or less.
Please keep in mind, this is just my opinion and my price check is based on market trends and what is most likely causing the lull.
Anything that can be dyed with a normal tub - the color can be replicated from my experience. I've seen folks trying to sell "sigil" clothing in the past. Everything else I think can't be replicated color wise, but darn its pretty close.