Stan,
There is no standard answer for your question. There are many variables that go into any value calculation for used RV tires. Since most of the used truck tires go on commercial long haul trailers that almost never run 295/80 22.5 tires, that lowers their demand considerably. Also, the age of the tires will figure into their value. No commercial driver will run aged out steer tires on his tractor for the same reason that you are replacing them. However if you were running 11/R/22.5 or 295/75 22.5 tires, even though they have a lower load rating, they are in demand as trailer tires.
When I replaced the original 11/R/22.5 tires on my 2000 Marquis at 3 years of age because they were overloaded, Les Schwab in Bend gave me $150 per tire credit for them towards the new 295/80 22.5 replacements, and they had them sold and installed on a commercial trailer before I even paid my bill.
To put it simply, your aged out 295/80 tires may have some value to a very few people, but it will be rare to find a truck tire shop that will want them bad enough to pay for them.
Gerald