Large tires are never inexpensive, but check out Hankook (Korean and a respected international brand). It's an excellent tire at a decent price. Kumho is another respected Korean brand with good prices. Cooper & Firestone make some moderately priced 19.5's too.
He might do better price-wise with a Chinese tire, e.g. Gladiator, Triangle, etc. However the quality is often inconsistent and the risk of getting an out-of-round tire or an early life failure is higher than with better brands.
225/70R19.5 is a close equivalent size and probably easier to find at lower prices. See this Goodyear web page for information on substituting that size.
http://www.goodyearrvtires.com/size-conversions.aspx