Classes and books can definitely be expensive. I would suggest visiting your local public library and just checking out everything they have to offer in the art section on drawing. Some ones I really like from personal experience:
-Picture this by Molly Bang (for composition). Very simplified but makes valid points
-Drawing on the right side of the brain by Betty Edwards (general drawing) Full of neat exercises to expand your perspectives
-Color and Light by James Gurney possibly the best book you could ever use - really comprehensive once you get to that point
-Any sort of "classical anatomy for artists" type books
Also any book from Andrew Loomis - an excellent illustrator who had a tendency to make things really understandable/digestible. These are really old so you can maybe even find these available as free pdfs online (or send me your email and I can send them to you).
Additionally sketching from life is so important, whether that means going to local life drawing sessions and pitching in a few bucks towards the model or doing landscapes and still life drawings. Learning the rules and fundamentals helps you break and warp them if you want to stylize things later on.