Learn Dutch: Het was de prijs die echt belachelijk was. - It was the price that was really ridiculous.

This lesson teaches using wat after neuter (het) words and superlatives (like het mooiste wat...). However, in this sentence, the relative pronoun refers back to de prijs, which is a regular de-word. For de-words, you must always use the standard relative pronoun die.

Why does the sentence start with Het was if de prijs is a de-word?

Het is acting as a 'dummy subject' here, just like 'It' does in the English sentence 'It was the price...'. When you introduce or identify a noun using a form of zijn (to be), Dutch always uses Het is or Het was, even if the noun that follows is a de-word or plural.

Why does the second was go at the very end of the sentence?

The phrase die echt belachelijk was is a relative clause (it gives more information about de prijs). A relative clause is a type of subclause, and in Dutch subclauses, all conjugated verbs are pushed to the end of the clause.

Is echt used differently here than when it means 'real'?