I have long been interested in cosmology, and I took a course with the same title in undergrad. We used Liddle's book An Introduction to Modern Cosmology which I thought was pretty good, but it was relatively short. I have knowledge of mathematics and physics up to early graduate level (got my BS in Physics, minored in Math and have had some math courses from grad school engineering). What I am looking for are some good books that aren't too expensive (<$150 would be an estimate) that would allow me to learn and understand cosmology at a deeper level. Any recommendations?