I don’t doubt the effectiveness of this new gadget, but we simply don’t have the money to buy it.
Explanation:
The word ”effectiveness” means a degree to which something is successful in making a result that is desired. In other words, something with effectiveness is something that successfully produces a result that a person wants/desires. It makes a desired change/effect for the person using it. The effect is rooted within the word too, so that is why it’s the appropriate word to use.
