The penalty for searching without a warrant is that evidence acquired is inadmissible. Sometimes. Sometimes not even that. Typically, that's fucking it. So it doesn't really matter that the search was illegal once the property is returned. Mostly, the penalties for the police are just political ones.
If there are some provable damages, the person who's civil rights were damaged might be able to sue, though with qualified immunity even that is a very, very uphill battle. SCOTUS rules against plaintiffs in cases like that routinely because the SCOTUS is very, very pro-police. They routinely rule that making things harder for the police & prosecutors is too high a price to pay for protecting civil rights. See, for example, Van Buren vs US or Arizona v. Gant.