If you don't know where to look, bento can be difficult to find-- and expensive! Small bento boxes on ebay or any specialty store can easily run $15-20... for something that holds one or two cups.
My first bento order was from All Things for Sale. Overall, they have good prices (although some expensive bento boxes) and a good selection. If you order more than $50, they'll send a free gift, and flat-rate shipping (from the U.S.! Many bento sites have foreign shipping) is only $6. (ETA... I now have an associates account with ATFS. You can use my link on the right sidebar to order so I'll get credit).
The best (cheapest and widest selection) bento store I've found is Fit. It's an online Japanese dollar (well, two dollar) store, and all bentos are $2-4. Lots of great accessories, too! However, if you're looking for character bento boxes, you won't find them here.
A few other stores you might want to check out:
- Jbox. Lots of cute bentos, but the accessories especially are on the more expensive side.
- Bento & Co. All bento. Lots of cool stuff, expensive, but you can find a few deals. Lots of adult (and larger-sized) bentos, though! And, everything is high quality, microwave and dishwasher-safe. Shipping is expensive as well.
- Amazon has a few bento supplies, mostly boxes... see my sidebar there.
- It's also possible to find some good deals on ebay... I found two character boxes, shipping included, for $13, from Japan. Most things tend to be overpriced, however.
Ordering bento is fun-- gift cards I'd bought from earning Swagbucks and money I made taking surveys online financed almost all of my bento gear!