There are plenty. There have been around 70 books reviewed in BMCR since 1990, a bit over two a year (the actual rate will be higher than that: it took a few years at the start there for BMCR to really get going; on the other hand most of them are new editions, commentaries, and translations of the plays).

For a general book targetted at a non-specialist audience and in a sensible price range, there's only a couple of options:

• Finglass, Patrick 2019. Sophocles. New surveys in the classics 44. Cambridge University Press.
• Garvie, A. F. 2005. The Plays of Sophocles. Duckworth.

The Blackwell companion is in a higher price range, and the Brill companion is far too expensive for most individuals.

There are a bunch of other interesting ones but it entirely depends on what topics someone wants to read about, and how full-on scholarly their taste is. Everyone will have their own preferences. I'll just suggest a couple more:

1. Austin, Norman 2011. Sophocles' Philoctetes and the great soul robbery. University of Wisconsin Press.

Probably the best book for someone interested in the psychology of Sophocles' characters, without being too jargon-heavy.

2. Sommerstein, A. H. et al. 2006. Sophocles. Selected fragmentary plays vol. 1. Aris & Phillips Classical Texts. Oxbow.

It's always exciting to find out that a great author wrote more things than you realised. Here's your chance with Sophocles.

There are plenty more academically oriented books, and let's face it academics and students are the main audience for books about Sophocles. The ones I've listed should be perfectly accessible to someone with a generalist interest.

In light of that, I do want to emphasise in closing that the question absolutely is not self-explanatory. There's a range of books available: if I'm going to make suggestions, I've got to make guesses and assumptions about where you're coming from and what your interests might be.