Depends totally upon where you pick up, how long you need it, and where you will drop it off. You can use their site to figure what your cost will be and add or subtract add-ons, change dates, etc until you get what you are happy with.
Depends on where you live, what size the truck is, how long you need it for and if you are going to return it to the same place or leave it in another city.
Last year I remember the u-hauls running around here that had a sign on them they charged $19 a day. I imagine you pay for the gas when you pick it up and then fill it up before you return it to U-haul. I don't know if there is a deposit though (I know places that rent cars out for the day or weekend want a deposit of a couple hundred) but that's why you put things on a credit card.
You'd need to also rent one of those carts to put boxes on to save your back. And you'd probably need to ask people to help you move (friends) for an hour or two and buy the beer.
I can't remember the name of the company (there are a few) that you call them and they drop off this big wooden box, you take your time filling that box (it's like a rental truck) and then call them back to pick it up and either take it to their warehouse or to drop it off at the place you've moved to. Still you'd need to ask a couple of friends, or just your family take their time in filling it (maiybe over a day or two).
If it's a local move, it's under $100, most likely under $50. If you are moving out of state it will cost more. If it's a major move out of state, contact ABF at upack.com, you fill a 26 foot long trailer that has more space than a 26 foot long truck, and they deliver it to the location of your choice. They can even store it for you.
Basic day rate ($21 for the 18 footer here) and then a certain price per mile (and you have to pay for filling the gas tank back up). If you have car insurance you do not have to pay for extra insurance on the rental.