Good seed is usually worth the price. Perhaps one wants to grow something just to fill the space, as in a cover crop, or right after the planting season one may find bargain prices for just the right variety. After planting time stores want to clear the shelves and may offer seeds are greatly reduced prices. However there are good reasons to pay a bit more and order from a seed company.
Most seed sold in box stores is “generic.”‘
The most generic I’ve seen even failed to list an actual variety name! Hence, one could pick up a packet of “beans” or a packet of “pickling cucumbers.”
Box Stores Usually Can’t Address Local Conditions.
Their seed is best sown in “average” North American conditions. Maybe you live where conditions are considered average. I certainly don’t! If I planted pole beans from most box store seed packets, I might end up with few or almost no harvest during the heat of summer! I need to plant varieties which can tolerate heat and drought or else produce in a very short period of time. So, if I want the best seed for my garden, I would do well to research and order varieties which fit these criteria. There are more in seed catalogs and on-line, than in my local seed racks.
Seed Companies Cater to More Specialized Needs and Tastes
That’s not me! I have specific preferences when it comes to beans, tomatoes, squash, peppers, etc. My preferences are specific enough that it could be difficult to find them on a rack in the store, but I can find them if I am willing to look around and order them ahead of time. So if I want a variety which will give me the specific flavor, texture and colors I’m looking for, I will pay the price, research and order it.

Being a seed saver makes me more inclined to pay the price for “just the right variety.”
You see, I tend to grow and reproduce seed for use across the years. If I’m going to do this, why would I want to grow something run-of-the-mill? I’d rather get that special variety and reproduce that! Additionally, as a seed saver, I have to recognize that seed companies play a significant role in preservation of rare or endangered varieties. Most companies need to sell seeds in order to stay in business. Hence, I give them my business. We have a mutually beneficial relationship!
Victory Seeds provides a great example of the good preserved by seed companies.
Review of Victory Seeds with link to discussion of Ralph’s Italian Heirloom Pole Bean
Back in the 1980s I was given seed to Ralph’s Italian Heirloom, a good Romano style pole bean. I distributed it through the Seed Savers Exchange, but eventually I lost my seed. Recently a fair number of gardeners have all started trying to revive this bean. Guess what? Victory Seeds has it in their frozen seed bank and will bring it back. We need seed companies like this if we’re going to preserve the most varieties possible. When I pay such a company for a packet of seed I support seed preservation.

If you appreciate preservation of good varieties, consider getting some really good seed through some good seed companies.