I bought one 2 years ago with about the same sized trunk from Brussel's Bonsai. Unfortunately it seems they have sold out of those.
This one isn't as neaely as big a trunk but IMO a better tree with less work needed to see its potential than the one you were looking at. It's a lot cheaper too.
What I'm not sure of is if the tree pictured is the actual tree you will get. You can contact them with your price range and see if they will send you some pictures.
Trident Maples produce vibrant green foliage in the spring and a bright orange in the fall. They are among the most popular deciduous bonsais with quick growth.
brusselsbonsai.com