The voyager probes had 450 watt of total electrical power at launch, supplied by 3 RTGs. The plutonium alone in one of those RTG units (4.5kg) would easily cost $10M.

And it's the type of thing that is only used by government programs, very dangerous to handle, and which requires a whole specialized industry to produce. The accounting gets complicated. I wouldn't be surprised by a $100M cost per RTG unit.

Generally it'd be more efficient to build a nuclear power plant with the materials from the RTG, and power many houses.

You can steal some from russian lighthouses....on your own risk.

The Cassini probe used about 60 pounds of plutonium-238 for its RTGs, at a cost of around $200 million for just the plutonium.