I am grateful to Ben White for drawing my attention to Bentley Layton's new book:
Coptic in 20 Lessons
Introduction to Sahidic Coptic With Exercises & Vocabularies
That link is to the Peeters catalogue on the book, which also has a table of contents (PDF). Up until now, the only realistic option for an introductory grammar was Lambdin, so I am excited about the new Layton book. I don't have a copy yet, but will report on it as soon as I have one. Amazon have it for $34. Layton is "the man" when it comes to Coptic, so the publication of this looks like very good news.