There are coops here also and some are on both, Like the Iris Coop. I spent a lot of time on Mamajacks this year purchasing plants for a butterfly garden I was planning, she is on Cubits. Then I also bought Hostas and Daylilies and Tropicals from other people who team up with her. Like Bentley Gardens and Bayou Blooms, I got great plants from them.
On ATP, I have gotten lots of stuff also, sometimes people will just pop up on the Forum (coops) and offer a great deal on a box of plants or offer Iris for 3.00 a piece like Dee. Watch the forum and you might be surprised at what pops up.
Also, early in spring a lady named SueTaynor was selling Hosta roots for 2.50 and they were real good size. I got some nice plants from her.
http://garden.org/forums/view/...