Thankfully, I'm posting this on behalf of a friend (not me!) who is experiencing this as a first-time home owner. He's used traps but they keep coming. An exterminator would cost him about $300 and set more elaborate traps that they would have to monitor for 3 months to ween the problem but that doesn't right to me. Aren't there people who could get rid of them instantly and also seal all the potential entrances, therefore eliminating the problem at the source? My guess is this happens every year at that house so I'd rather my buddy fix this permanently the first time rather than try to go at it half-assed and only getting rid of the mice for this year. Thanks to all who can provide input on this.