Renting a Tow Dolly costs between $45.00 to $60.00 per day depending on who you rent the Tow Dolly from.
When I used to rent a Tow Dolly from U Haul I would pay $45.00 per day which was reasonable and not too expensive.
But if you want to use the Tow Dolly for a week or a few more days and go out of state with the Tow Dolly rental then it can add up in costs.
Using a Tow Dolly from U Haul for up to a week and traveling out of state can cost up to $400.00 which is almost the cost of buying your own Tow Dolly.
You can sometimes find a cheap used Tow Dolly through Craigslist if you have a more of a need for use of a Tow Dolly.