If there are only specific areas where you use wifi, you might find something like Llama useful - you do low power geolocation by 'learning' the cell towers at

If there are only specific areas where you use wifi, you might find something like Llama useful - you do low power geolocation by 'learning' the cell towers at each location, then set actions for arrival or departure from locations. The default rules may do more than you want (e.g fiddling with volume), but you can easily strip that back to just wifi control.