I live in a mobile home that has about 20 inches of crawl space and want to run a telephone line from one side to the other, below the floor–a distance of about 24 feet.
Both access doors are on the opposite wall from where I want the line to come up into a room.
Unfortunately, the ground under the crawl space is covered with “decorative” white rock, which is murder to crawl upon, on your hands and knees. And in the middle there is a line of cinder blocks (admittedly with big holes in the sides) running along the long axis of the mobile home.
What’s the best way to run the line below the floor? Borrow a pole trimmer? Fill a garden hose with dowel rods? 
kneepads and thick gloves?
Can you buy or borrow a fishtape? Might suit your needs. It sounds, though, as though you may have to crawl under at least at the point you want to feed the line back up (although you may be able to come up with a creative solution; you know the specifics of your situation far better than I).
I’ve always thought that an easy way to get a wire across a distance that can’t be easily crossed by a person would be to tie a string to an arrow and shoot it across with a bow, then tie the end of the wire to the string and pull it across. The only problem is that the wire cannot be secured along its length, only at the ends.
You’re on the verge of a good idea with the hose: cement enough sections of PVC pipe together and put the wire inside so it will be protected.
I would just use a fish tape, iuse them all the time for pulling wires, and with that clearance between the ground and access hole, it should be easy for you to grab the other end when fed through. Alternatively, I’ve used pieces of gray wire conduit, as it is pretty flexible as well, and connects as easily as it diconnects (cheap too!)
You’re not the first person to come up with this sort of idea.
Greenlee makes a nifty little gadget that looks like a cross between a kid’s dart gun and a fishing reel. Well made, but kinda pricey.
Bow & arrow, crossbow, slingshot all work well. A guy I worked with took his son’s R/C jeep and drove it across the ceiling to pull a wire. 
Can you remove the baseboard molding and run it behind there? I do this all the time, and you can even run it behind casing that surround doorways.