Not to put you off or anything but there is a better source for HDT info. Go to the escappees web site, http://www.rvnetwork.com/index.php?
and then scroll down to the HDT section. You do not have to be a member of the club to read it and joining the forum is free.
In short the cost is all relative. It depends on how new or how many miles are on the truck. The condition of the unit will determine how much maintenance is needed. I have a 2000 with half a million miles and have had very little done with the engine or running gear. A friend of mine has a 95 with well over a million miles and he also has had little maintenance done. Both of the trucks were in good shape when we bought them. We both have the trucks checked and serviced (oil lube and brake adjustment) annually at a local shop in Tucson. It cost me about $700.00 the last time but I had a couple minor items taken care of at the same time. There are no tune up's per se. You can get what's called an "overhead" which is a valve adjustment, jake brake adjustment and clean the injectors about every 100,000 miles.
The tires last a long time as long as they are new ones. Mine have over 55,000 miles on them and are still going strong. I did replace the steer tires because of an alignment problem that caused early wear after I had some front end work done. They wouldn't ballance properly and rather than put up with it I changed them.
Cost to set up as a toter depends on you. I did not single the rear axles out. I saw no reason to do so as it rides fine and I like having the abililty to go to 8 wheel drive in loose surface conditions. I also did not go to spend big $ on getting a custon bed put on it. I had a flat diamond plate bed fabricated with fenders for under $3500.00 rather than the heavy full box style that most folks get. The average cost for one of those is between $10,000 and $20,000.
You can either go big $ or low budget on these, it's up to you and your pocket book and how willing you are to look for the best buy.