For 4wheeler size tires your looking at around $375-$450 a pop... all depends on the capacity of the tire. You only want to do it with tires that are in good shape. Put it in older tires and it will tear them apart quick. Your also going to add ALOT of weight to whatever this is so keep the size of your transmission/gears in mind
I have seen them back tires foamed on UTV. They rear axle can handle the extra weight better than the fronts. The tire shop I used told me that they hunters would foam a new set of rear tires and then use them only during deer season in West Texas. Take them off and store them the rest of the year. I just keep a plug kit and 12volt air compressor in my Ranger when I hunt West Texas.