If you don't want to work on the feature (i.e. you're uninterested), it's better to be honest about it.

If you do want to work on it, but your time would be better spent on anything else, and you're willing to work on it for money, first ask if the requester is interested in paying for it and then give your estimate.

The difference between a feature request and a client approaching a freelancer/company is that in the latter case, the other party initiates the conversation with a clear expectation of paying — they only have to decide if they like the terms and price.

Being uninterested to do it for free: Yes. But when I am interested to do it for money, giving an upfront estimate based on the hourly rate is the most honest way imaginable to me.