If your time is worthless, the least expensive option will be to produce your own food.
If your time has value, the least expensive option will be to buy from a commercial kitchen.
What is reasonable is subjective and depends on the experience you want to have.
If you enjoy cooking as a hobby and are able to afford the high cost of operating your own kitchen, then that will be the only reasonable choice in your mind, and in that case the grocery store will provide a pretty nice experience in simulating wholesale distribution in quantities the hobbyist can manage.
A number of reports suggest that commercial kitchen use is on the decline, so, assuming people aren't eating less, it seems that cooking is gaining in interest as a hobby. Thus it stands to reason that the grocery store can charge that elevated interest more than in times past. That's just basic supply and demand.
