Check out local yahoo groups, Freecycle for one, I got over 200 of them for free last week on there
Also, eggcartons. com does have CHEAP ones, you have to buy the mis-printed ones, I bought a bunch there that were mis-printed and had free shipping, was about $15
FYI..... check local and state regs on carton use. Here in FL you can not reuse printed cartons from another source (especially those marked with grading on them)
I bought 50 cartons you can break in half since I give away my eggs 1/2 dozen at a time. I used the site found here: The Egg Carton Store. Free shipping. I made my own label for fun, which I print out on my computer and cut it and tape it to the carton. Red Star Lady Eggs. Photo on my photo album. lol
At first people saved me cartons, which is free, but I found they are a pain for me to store, so I bought my own as above. They are packed flat in a small box and I can peel off a one dozen carton and break it in half when I need it. I think they were in the range of $34 for 50. I like cardboard cartons. Styrofoam give me the heebie jeebies (the feel and sound of it).
i sell eggs, and what i have regulars do is this: i have THEM have an empty carton or two ready, then i transfer MY eggs out of the carton i have, into their carton, they keep their cartons all the time, i just transfer eggs to them!