Seriously. Where do folks get the idea that Dahlias tend to be too expensive? The rewards of watching beautiful dahlias bloom are priceless. In your friend's zone, she wouldn't have the maintenance of digging them up every year. She can dig and divide every couple of years, and have many, many more plants for her garden as well as sharing the extra tubers with friends. Isn't that really the joy of having a cutting garden should be?

I have no idea what your friend should grow in her cutting garden. Perhaps she should visit a nearby botanical garden for ideas.

Sea Turtle
Sunflowers, zinnias and celosia are easy enough.
I think the issue in Zone 9 with dahlias will be disease
problems and not cost of planting or maintenance.

You can grow dahlias from seed with 60% success, you need to start them inside Feb. or out when weather is in 70,s Also zinnias marigolds , sun. , cosmos , cornflowers, carnations, dianthus, african daiseys. The list goes on and on .