there's absolutely loads of them out there which will allow this.
and you are right.... why blast a signal out to places where its not needed.
there also the issue of quality as well. not a lot of people realise that transmitting on the same channel with overlapping networks can reduce performance eg you are on channel 6 and so is your neighbour.
however, if its down to cost and you'd rather no spend, then the above tips are good enough and really should be standard anyway.