Depending on where you are looking to go to is sometimes less expensive to rent for in town then it is to do a one way, if it's not a major inconvenience and the difference in the price is low enough to make it worth while then sometimes the price is less to rent and bring it back. It is no problem to get both prices in the same call to compare.
Your best bet is to call them directly and ask them. You might save round trip if they give you a deal or have a special. I know there's a fee after a certain amount of miles and you have to fill the gas tank up before returning the truck.
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