Merci beaucoup, everyone! Interestingly, at one point in my searching RCI the Domain Gauvidon did come up, but I passed. From searching VRBO, there seem to be many very reasonable and 'tres charmant' options in the Dordogne area. Thanks too for your links, Conan.
We fly into Bordeaux from Barcelona and DD/DSiL from Marrakech. Their flight gets 90 min. in after ours at @5:30 pm, so I think for that night we will stay in a hotel in the Libourne/St. Emilion area, then off to near Sarlat for the remaining 4 nights until our exchange week at Royal Regency.
I've several guidebooks on hand currently, but returned Rick Steves to the library- I did find his info on the various caves most helpful although he made it seem nigh unto impossible to visit some of them such as Grotte de Rouffignac and Grotte de Font de Gaume due to limited spots and no option to pre-purchase tickets. Luckily we have over 8 months to plan for the cave tours. And mid-week in September should be relatively light on tourists like us!