Online booksellers

I <3 online booksellers. The instructor recommended two dictionaries: Al-Mawrid, which is alphabetical; and Hans Wehr, which is based on the 3 letter root of Arabic words. New, the dictionaries cost ~$75 and $45 each, but are worth investing in if I plan to continue with Arabic...and I do. So I checked out a couple of online booksellers and found copies for sale: instead of $120, I'm paying ~$70. Yay for my bank balance!

I'm perplexed about dual nouns. I shouldn't be -- Russian has a bunch of nouns that change based on number: one, two-four, then five +.