What are my best & least expensive options to get this done? That's what I need to know.
The post from seige101 above gave you your answer.. The two common setups are the Reliance Controls style transfer switch box, or a a panel interlock backfeed breaker.
The interlock breaker is cheapest in terms of materials (maybe $50-75 for the interlock kit and another $100-200 for the input box and wiring), but you need to either get a big gen to run the whole house (prob need a BIG one for the well pump anyway) or know to turn off a lot of loads before switching over. And with the entire house disconnected from the street you will only know the power came back by watching for your neighbors lights to come on.
The transfer panel is a bit more cost of materials (maybe $300-400 with wiring, etc) but lets you selectively choose circuits to power and works with smaller gensets better.
Add a few hours labor by a pro electrician and permitting fees to either.
E