Combination of "ludicrous" and "lucrative", it denotes something that is totally ridiculous but actually produces a tidy sum in the end.
Two examples of ludicrative actions were people's buying dollar-coins with a credit card and then using the coins to pay off the card to earn card-perks, and the infamous "obsessive coupon-cutter" dude who bought many thousands of foil-sealed cups of chocolate pudding to earn astronomically-voluminous frequent-flyer miles.
A Shackteau is a humble, weather-beaten, structurally questionable shelter located in a spectacular or highly coveted place—Wales, Jackson Hole, Sun Valley, Crested Butte, coastal Maine, the Alps—where the building itself may be worth almost nothing, but the dirt, view, access, and mythology make it absurdly valuable.
In use:
Shackteâu - We thought it was an abandoned shed until the realtor called it a rare alpine Shackteâu with unobstructed views and listed it for $2 million.