I used to buy 6 packs of bedding begonias and put them in individual pots in my classroom windows. They were pretty much nonstop bloomers, and oh so cheap. Geraniums are almost as cheap, but the do need a little more care on cleaning off blossoms. Angelwing (aka Dragonwing) begonias cost more, but they are so beautiful, so cheerful, I think.
Some vets might like a novelty plant like 'Firesticks' euphorbia.
Or Aeonium, or maybe mother of Thousands, (
Mother of Thousands (Kalanchoe daigremontiana 'Jaws of Life')) There's lots of succulents that make good houseplants, and they should be readily available in Arizona.
Swedish ivy is always a good easy window plant, too.
How about scented geraniums? They like it hot and dry.
This brings back memories of my uncle and my grandparents pointing out their windowsill plants every time I went to visit them. So glad you are doing this.