Hard to give one blanket number because I am more okay giving attention to someone I follow, for instance, than I am with giving it to advertisers. Ideally the amount could be set different depending on whether or not I follow the account. If I follow an account I would be okay with them including messages in any zaps 100 sats and above. If I don’t follow an account, anything 1000 sats and above.
Even better would be a default amount, and then let me adjust it on a per account basis. So maybe I’m okay with you sending me zap messages of any size zap, so I’d remove the restriction on your profile in my settings.