What is the value of a Monticello nickel with no date that is double struck?

If it is a Mint error it may be worth a few dollars, take it to a coin dealer to see if it has any value.

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It's called a Jefferson nickel rather than a Monticello nickel. If by "double struck" you mean that Monticello is on both sides (which would account for the lack of a date) what you have is a novelty item called a magician's coin. There's more information at the question "What is a double headed nickel worth?"