A substantive edit is what I call a combination of everything. It's an in-depth line edit that deals with everything from grammar to character arcs and development and how well that development is represented through the narrative and dialogue. I focus on themes, plots, sub-plots, among many other issues (grammar included).
A substantive edit is a very thorough edit conducted line by line. Like a content edit, a substantive edit may require surgery. Rephrasing/moving passages. I often make suggestions and help to guide the author.
Costs for substantive edits:
A 20,000 word manuscript would cost between $600-$800.
A 50,00 word manuscript could cost between $800-$1200.
An 80,000 word manuscript starts at $1400 and can go up to over $2,000.
Anything over 100,000 words will start at $1600 and can go up to $5,000 depending on the amount of work needed.