Im not sure as there is a way. I think lightnings list maker has the option to include unpriced so you could use that? Maybe make a list with unpriced and a list without and compare? I think it might default them to the top or bottom of the list anyway.
Lightnings list maker puts unpriced items at the top first... Separated by a border, which is easy to see. That'll be your best bet.. I don't know how to use the other site.. I'm too lazy for that
I tried sorting by price and it didnt seem to work. I think it excludes them as they have no price to be sorted by.
The only way to get the Unpriced Items is to go through all the items in a certain category. That's why the 'Unpriced Items' option takes forever - it gets all the items of a selected category and then goes back and removes the ones that are below your minimum price/rarity