You are right, those B/stone 250's are pricey even on OOIDA site for 22.5's. I have a mixed bag of tires under my car trailer now & have one or two R250's in the 19.5, the price on those wasn't so bad. Also found I can get them in 16 ply. So thanks for making me look at that sheet. FWIW, the B/stone is wearing better than anything else, BUT have no clue as to how long anything has been under there. Anyway, wanted 22.5's on this trailer, but buying used negates what you can order. If I had them though, the ST230's were the best bang for buck I could find a year or so ago with a different trailer. http://www.bfgoodrichtrucktires.com/bfgtruck/tires/tireInfo.do?tread=ST230
I have had very good luck with Double Coin. They have a very thick tread design and I have gotten very good service from them. I have run Dunlops and but they are much more expensive than Double Coin. Love's sells Double Coin and you may find others who do, as well. I buy them from a local distributor and can usually get them for about $50 or more less than at Love's. I used to only buy the major US brands, but they don't usually stand behind their product and want to charge twice as much as I can buy less expensive imports. There are also several other brands from Japan and Korea that are good and less expensive. Yokohama is a good tire. At one time I preferred Bridgestone tires. I can't see paying $600 for a tire when I can buy for half that amount. I have also had good service from Goodyear recaps. They have one specifically designed for spread axles. Unless you run at 80 mph all the time you could get good wear from them. I have a friend who has been running recaps for a number of years with great success. The key is to watch your air pressure. If you normally driver around 65 or less then caps can work well for you. My friend drives at 65-70 most of the time.
I like the General S371 or the Continental HSR2 but I don't think your going to touch either of those for $400.
I wouldn't run the FS590 on a spread. That is a steer tire and I have found that I need a tire with a solid shoulder, the FS590 has a small rib on the outside. I have also ran the Yokohama RY023, it is a good tire but the cost per mile was more than the Bridgestone R250, because I got less miles out of them. I actually run the R250's on the front axle because it is the one that scrubs hard on my trailer. I run Yokohama RY587's on the rear and have had good luck with them. I have 175K on them and will replace them in the next 4 weeks.
I run the Michelin recaps made for a spread. I have my casing caped and the last 2 a bought 2 weeks a go cost me $219.40 a tire out the door. They hold up pretty good. Definatly not as long as a new tire but for thr price i can get 2 for the price of 1 new tire.
I ran for MRT spread axle caps for years on my flatbeds. It's the only cap I'd buy besides Les Schwab out west who did a seamless cap.