If you're talking about monetary value:
* Worthlessness
* Cheapness
* Insignificance
* Pricelessness (ironically, as it means something has no price, thus no monetary value)
If you're talking about importance or worth:
* Worthlessness
* Unimportance
* Futility
* Insignificance
* Meaninglessness
If you're talking about a personal value or belief:
* Disbelief
* Opposition
* Rejection
* Disregard
If you're talking about a value in a programming context (e.g., a variable):
* Reference (in some contexts, a variable can be a reference to a value, so the opposite would be the actual value itself)
Please provide more context so I can give you a more accurate antonym.