Not my area at all, sorry. I'm not fabulously wealthy.
Fingers crossed Mike M will pop in and give an intelligent comment, but values are very subjective.
The missing stopper might have a fairly drastic effect on price, I would think Lalique collectors are in an "echelon" where they want perfection, don't care about the actual cost, as it means little to them.
I'm not a seller - just a collector of studio glass, but enthusiastic and learning about all other kinds of glass.
My opinion is not particularly good when it comes to old, expensive stuff.