Affordable artwork abounds in the Etsy-era we're living in and even more so if you're poised with printer and ink at home. Jennifer of Salt and Paper designs artwork, largely with child-friendly themes, that is super affordable (about $4-5 or, in some cases, free like the Peep print above) and super customizable (choose any colors you want).
There are several color schemes of each design ready to go or you can use your cursor to choose exactly the colors and saturation you want for each element of the design. You purchase the PDF and print it out at home.
In addition to 8.5" x 11" prints, there are also designs for cards, stationery, calling cards, recipe cards and address labels. Above is a sampling, and you can find the whole collection at Salt and Paper.