The Secret's of Ms. Snickles Class. I read this book during college in my child's lit. class and I loved it. I LTS in second grade last year and they LOVED it.
Barnes and Noble can be a bit pricey. Do you have a half price books around you? A lot of times they have popular series like Magic Tree House, Junie B, etc for 2.00 a book. Also, don't forget ebay...search for second grade books and there will be some Lots of new books for less than a dollar a book.
I bought a lot of Berenstain Bear books off ebay last spring. My students loved them and they were great for AR/SRI tests. I got about thirty books for thirty dollars (shipping and handling included).
I've also found some great deals at local resale shops. I just take twenty bucks at a time, and I can usually get about forty books. I've been lucky too, only about ten of the books I bought don't have a quiz!
Also, what about the library? My local library will allow you, with a teacher account, to get a class collection of books to be dropped off at your school. They will send you a wide variety of leveled books that you get to keep for a month. Or if you are teaching a special topic, let them know, and they will gladly collect books for you. It's a great way to get cool books for read alouds.