Learn Spanish (Latin America): ¡Lo que cuestan esos cachivaches!

While ¡Cuánto cuestan esos cachivaches! is also correct, using ¡Lo que...! adds a bit more conversational flavor and emphasis. In exclamations, lo que followed by a verb stresses the extreme quantity or degree of that action. It translates closer to "The amount that those pieces of junk cost!"

Why is the subject (esos cachivaches) at the end of the sentence?

In Spanish exclamations, especially those starting with question words or structures like lo que, it is very common to invert the word order. Putting the verb (cuestan) right after the exclamation keeps the focus on the extreme degree of the cost, while the subject (esos cachivaches) gets placed at the end.

Could I use the lesson's other structure, la de, in this sentence instead?

Not directly, because lo que is used immediately before verbs (like cuestan). If you wanted to use la de to express an extreme amount here, you would need a noun right after it, such as: ¡La de dinero que cuestan esos cachivaches! (The amount of money those pieces of junk cost!).

What exactly does cachivaches mean?

It is a very common, informal word! A cachivache refers to a useless object, a piece of junk, a knick-knack, or an old gadget taking up space. It is a fun, slightly derogatory term you will hear across Latin America when someone complains about clutter or overpriced, useless items.