Some clubs in the lower leagues like Périgueux, Limoges and Tyrosse have plenty of cash to spend. Most of the other clubs are secure, but a few still struggle to survive. A few seasons ago we seen Gaillac fall from Pro D2 to Fédérale 3 and last season we seen RC Chalonnais fall from Fédérale 1 to 3 due to bankruptcy. I don't know if you can find a site for lower league finances, but I know these budget numbers for Pro D2 clubs are accurate.
Lyon OU - 8,19 million €
FC Grenoble Alpes Rugby - 7,45 million €
SC Albi - 6,83 million €
Section Paloise - 6,18 million €
US Dax - 6,14 million €
Union Bordeaux-Bègles - 5,43 million €
RC Narbonne - 5,23 million €
US Oyonnax - 4,55 million €
Tarbes Pyrénées - 4,50 million €
Stade Montois - 4,45 million €
US Colomiers - 4,20 million €
Pays d'Aix RC - 3,29 million €
US Carcassonne - 2,86 million €
Stade Aurillacois - 2,61 million €
FC Auch - 2,56 million €
CA Saint-Étienne - 2,03 million €