Go to Penzeys, get bulk spices and mix your own as needed. Their stuff is top quality. To save money, go to cub and buy the bulk packets of Cub-brand spices. Very, very cheap, you don’t pay for packaging, and they’re decent.
There’s some great seasoning recipes on the internet, most of which have less salt, fewer preservatives, and taste better IMO. Making your own also gives you the option of fine-tuning. You can adjust heat, salt-levels, or add fresh herbs that you can grow yourself. Most pre-made ones are already “finished”. You won’t be able to substitute for flavor against fresh thyme, rosemary, oregano, parsley, etc.
Store bought is great in a pinch, and the convenience is definitely nice. That said, you can make your own fish mix, taco meat seasoning, rib/shoulder rubs, and general seasonings for cheaper with no MSG or other preservatives.
Joel