You can save money by keeping leftover seed for use next season.
Most vegetable seed should last at least a couple of years, with the exception of parsnip, and some can last much longer. Before ordering new seed, check through this season's leftover packets and make a note of what is there for use next year. Store in a glass jar or plastic box in a cool, dry place. If you are unsure of the age of the seed, do a mini germination test on a piece of damp kitchen paper in a plastic box.