Did you mean page count? For the novels I read, 200-300 per volume seems common. This seems comparable to the English novels I have, so it feels like less money for roughly same amount of content.
Because many light novels come in series that are spread over several volumes, it's arguable that it costs more money to finish a story because you have to read all these volumes instead of one monolithic tome. I buy the volumes one by one as they are released and don't feel that the individual books are that expensive, but someone catching up on an old series might feel different.
If you mean physical size, the average English books does seem physically larger than the average Japanese book.
Because many light novels come in series that are spread over several volumes, it's arguable that it costs more money to finish a story because you have to read all these volumes instead of one monolithic tome. I buy the volumes one by one as they are released and don't feel that the individual books are that expensive, but someone catching up on an old series might feel different.
If you mean physical size, the average English books does seem physically larger than the average Japanese book.