OK, here's are some crazy thoughts. If I have read this properly it is only the halter and rope that cause the final problem.
Is there any chance you could put a neck collar on him? Would you be able to put a very tightly woven black cloth over his eyes? Or borrow a racing blinder and cover the eyes? A horse that can't see is not so likely to run.
Or, what about when you get close to him, can you put anything on his legs? If you have to get him out and you tie his two front legs together (as in hobbling), he can't run so fast for so long. Now, if this method sounds do-able at all, I'm hoping that one of the true cowboys here will give some input as to the safest way to do that because this horse might completely freak out with restriction on his legs.
If you can do some kind of hobbling, a combination of hobbling and blindfolding will allow you to get a halter on him. Then keep him blindfolded and put him in a trailer. Or better yet, you may then be able to afford a "regular" very soft sedation just to keep him manageable until he is moved.