Even with small plants shipping is expensive. It is hard to part with a $10 or $15 shipping fee for a $10 plant. But nurseries can't ship for less, plant material and dirt are heavy. I tried selling plants on Ebay one spring and found I was losing money with most sales because I underestimated shipping costs.
But I do order from one mail order catalogue regularly, Gilbert H. Wild and Son. They send me sale catalogues several times a year and the prices during these sales are unbeatable. For example, Stella de Oro daylily is always $1.oo, Happy Returns $2.00. And the plants are always strong and good sized. I have bought most of my daylilies from their sale catalogues and they have all been excellent plants.
I also buy my peony roots from their sale catalogue, very reasonable prices and their roots are larger than several other catalogues I have tried that sell roots for two or three times the price. I like to buy three roots of a peony variety and plant them together to get a big plant quickly so a good price is very important. I don't have the patience to wait for a little $30 root to grow into a decent sized plant in five years.
I think I will try their iris this year, World Premier with dark purple falls and white frilly tops is calling out to me.