Welcome to Tnet. Nice find.
What you have is a marble topped drop center vanity. W. D. Comstock was the retailer. Look on the back/inside of the drawers for a possible makers tag/stamp.
This type of furniture was pretty common for the time among middle/upper middle class.
Having all three marbles is a very good thing. I think if you look on the top of the mirror case you will find three holes for missing finials. The missing drawers and drawer pulls reduce the value considerably. They can be replaced but a good match will be pricey.
I think you will find the mirror case and the vanity are not a pair. The mirror case appears to be late Victorian (1880s - 1890s) and the vanity with wooden drawer pulls (not Victorian) a bit later in the 1900 - 1920 time frame. If you look closely I think you will see the old mirror mounting brackets have left a different set of holes from the ones on your mirror case.
Value depends greatly on the manufacturer and of course condition. The late Victorian mirror case is not very elaborate and appears to be refinished. There is probably a modern mirror glass as well so not much buyer interest or value there. The drop center vanity is still desirable. If it's a good maker, has not been refinished, the marbles match and are unbroken/chipped you could be in the $1000 range. A famous maker could take it above that.
I suspect both pieces have been refinished. To get a better idea of value run it by a good auction house that deals in furniture from that era. Auction houses have no reason to lowball you or inflate the value and they deal with more furniture than any collector or antique retailer will ever see.