Need app suggestion - auto switching 3g on/off depending on wifi connection

Long story short - my home doesn't get an especially good 3g connection. It does get a good 2g connection though, and it has wifi anyway.

Do you have any suggestions for an app which would switch off 3g whenever I'm connected to my home wifi, and switch it on again once I leave the house?

Running stock 4.2.2 if that matters.

Since all I want it to do is this one this

1. I don't really want to spend loads on it
2. it doesn't matter if the UI sux.

You people are wonderful.