Whoa. Before I really get started, I just found a chemistry textbook that is selling new for $214.64, and that's discounted from the list price of $299.95. It's got some fairly good (thought not universally so) reviews, but still. Three hundred dollars for one book? Yowsa!
Well, for those who do like the addition of a not-only-online textbook to round out their studies but don't want to spend quite that much on a single book, here are some more reasonably priced suggestions.
Chemistry: An Introduction to General, Organic, & Biological Chemistry (10th Edition) - starting used at $12.98.
Chemistry, 10th Edition - starting used at $9.00.
Chemistry: The Molecular Nature of Matter and Change - starting used at $8.69.
Foundations of College Chemistry - starting used at $6.99.
World of Chemistry: Essentials - starting used at $0.01
And this isn't a textbook, but I personally recommend it to anyone struggling with chemistry concepts: Homework Helpers: Chemistry - starting used at $11.00. Or, you could purchase the previous edition here, starting used at just 1 cent. I actually have the first edition and found it to be an excellent resource for basic chemistry concepts.
I'm going to take a guess and say, as far as sciences go, chemistry isn't one of the more popular choices at the college level. I can usually find plenty of textbooks for a specific subject that are priced used for a few dollars or less. That obviously wasn't the case here. Please note that the above books are not listed in any particular order, and it's simple coincidence that they are priced in descending order. Also, I do not personally own all of them (only the World of Chemistry book and the Homework Helpers one), so I can't recommend them in particular. Use your own discretion if you decide to purchase anything. From what I saw, Foundations of College Chemistry had the most favorable reviews, aside from the well-deserved accolades for the Homework Helpers book.