The value of ordinary cavalry is double the value of the rider including his equipment, plus a variable bonus for his mount. Characters don't double in cost but pay only the fixed bonus for their mounts instead.
Mount  | Points  | 
Horse  | Rider x 2  | 
Warhorse  | Rider x 2 + 3  | 
Giant Wolf  | Rider x 2 + 4  | 
Elven Steed  | Rider x 2 + 3  | 
Warboar  | Rider x 2 + 8  |