Products like Dynamic Literacy WordBuildOnline work well with our only child status because it's an inexpensive price for as long as needed to complete the chosen level. This way we can take our time, and even spread it across grades if needed.
I try to find products that I can resale if needed or possible, especially if we find it just hasn't worked well with us. Not all vendors allow for resale, so always be sure to check with the copyright before doing so. I want to get the best bang for my buck, and get long use out of everything we use. Since we won't be reusing it in the future, I can often get a premium used price out of anything we sell because it has only been used once. On the flip side, I can also easily buy the score keys or non-consumables and save money by purchasing only the consumables new for several products.