Due to frequent power outages in my area lately I am planning on buying a 3500/3000 gas genset.I am on a fixed income which limits what I can spend.I don't have the money for a transfer panel.I have seen genset interlocks for about $150.I have a sqaure D homeline 100 amp service panel.The problem is that there's no room for the additional generator backfeed breaker.Is it possible to have an electrician wire a subpanel to my main service panel allowing me to use the interlock or would I need to upgrade the main panel?I can't afford a new service panel.I have seen single circuit furnace transfer switch's for about $100.Would either need to be permitted and inspected?I only need enough power for the fridge,furnace and some lights.Any advice would be greatly appeciated.