These characters combine to create a powerful image: a seller asking for (要) a price (价) so high that it fills (漫) the entire sky (天).
漫天要价 is a cornerstone concept for understanding Chinese bargaining culture. In many Western countries, especially in retail, prices are fixed. Haggling is rare and sometimes seen as rude. The price tag is the final offer. In China, particularly in traditional markets, tourist shops, or when dealing with private vendors, the first price quoted is often just a suggestion—an opening move in a negotiation “game.” This opening move is frequently a case of 漫天要价.
This idiom is alive and well in modern China, though its context is important.