pipe dream

pipe dream  {n.},  {informal}

Нереализуемая, финансово несостоятельная, беспочвенная мечта; невыполнимый план.

Joe went through the motions of pretending that he wanted to buy that $250,000 house, but his wife candidly told the real estate lady that it was just a pipe dream.

Ср.: PIE IN THE SKY.