Liquor stores, supermarkets, and even Craigslist and freecycle are good places to get boxes for free/cheep. One advice that I have, though, is to try to get the same dimensions - it makes it much easier to pack up the truck...
For 90% of the stuff you'll be packing, you just need general boxes. Things like the wardrobe boxes, or the dish/glassware inserts cover the other 10%.
Another place I've seen where you'd have to buy boxes is Costco. I was looking at theirs, and the price seemed to be pretty reasonable.
More advice: Pack books in SMALL boxes - if you use a normal 12x12 box, it'll be too heavy to comfortably carry!!!
(I was lucky - my company ships stuff all the time, so I was able to get my boxes from them. Turns out I didn't need them all, since we decided not to move.)
Final advice: Take the time to go through your stuff, and weed out stuff you don't use - why pack it up if you're not going to use it in your new place anyway??? (I gave away a LOT of stuff on freecycle)
BTW - congrats on the move!!