Dnil -- first thing: photograph the lot, front and back.
Get really good photographs. If you are incapable of getting good digital or film photographs, email me, and I will contact someone to photograph them for you.
Secondly, determine what the documents are. Catalog them by: Date, Issuing Authority and Recipient. (Old school diplomatic form is: (Issuing Authority/Recipient/Description/Action to be taken/Date and Authentication/Witnesses).
Once you determine what the documents are, you can start hunting for an authority who will know how to deal with the documents. If we're talking Texas documents, the state historical society will be able to inform you. They have professionals who deal with such documentation all the time.
Please note, they're not necessarily experts on the sale value of it, but if you ask me, the cash you're getting out of ebay is insignificant compared to the historical value. In any case, if they are worth something, you'd find that out from a discussion with a professional. At that point, the big auction houses (christies, sothebys) have professionals who can help you out.
As far as the 1.5 mil goes, don't get your hopes up. There are tons and tons of documents out there. Chances are their historical value is greater than their economic value. Of course, you can always sell them to some sucker. Just be sure you get photographs so some beancounter historian can make use of them. You have no idea how frustrating it is for an historian to know that a unique manuscript document is out there, but inaccessible because someone thought they could make a buck. Of course, it's worse for those of us who deal with really old stuff, because we know how few documents that enter private collections ever survive fires, floods, thefts and mutilations. I just lost one last year;oh the owner respected academia, and wanted to cut us a deal, $20k straight up. The university stated that was 350% over value and declined. It sold at Christies for $60k.
The kicker in that deal was that the manuscript was spotted by a Yale art history graduate student at a new england used book store on the $50 table.
She was stupid enough not to buy it, but to tell the bookstore owner what he had.
Anyway, I digress. Photograph your stuff. Catalog it. Find the authority involved. It's not wrong to want to profit from it -- just remember us historians and get those photos.