The two tires are apples vs oranges.
The R250 is a all steel carcass commercial grade LT tire that has a excellent reputation when used on 6k axles.
The Maxxis ST may be popular with some folks but a quick search come up with about a dozen Maxxis ST tire complaints just on this website. A google has even more complaints from a broad range of trailer types (not just RVs).
Cost ?? Sure the XPS and R250 are expensive as they are a commercial grade tire that weighs close to 56-58 lbs vs 35-37 lb for a ST tire.
Other excellent LT tire for 6k axles are of course the BFG Commercial HT as mentioned and the Firestone Transforce HT/Goodyear Wrangler HT/Uniroyal Laredo HD-H/cooper SRM II. These tires are a fabric carcass and a proven tire when used in a trailer position and 6k axles and smaller.
The LT tire is a bit taller/wider so do your measuring for proper clearance or let the tire dealer do it for you.