There use to be a VERY good place on trash and beach blvd however it closed down many years ago. If you want VERY Nice Bonsai tree I would go to Torrence its a little shop and is a Tree Bonsai Shop. If There is also a Shop off oh 605 if you really want to learn and what to get a nice size raw material tree I would go there. They have a nice selection of Japanese maple there. My Fav is the Red Dragon Japanese Maple but not a really good beginner tree I wouls stay away from red maple as a starter.
The one at Torrance is a true bonsai shop smaller a little more expensive but I better material or smaller.
One off of 605 has one of the All nursery its large a few acre in size. your best beat for a nice dia tree and a great price a tree that is around 3inch dia is around 100-200 (raw material bush) if I remember right also depends on spieces. This place is great but kinda like finding a needle in a hay stack for a nice workable tree. Most of their stuff is garden bush but has a lot of material for bonsai but you need to know what your looking for here. Take their class and have the teacher help you get your first tree. Also when you do bring a first aid kit. Juniper probably going to be your first tree and those little needle hurt and poke you right other the finger nail.
your classes (get the package deal on classes), tree, and some tools will run you around 400+ depending if you get cheap tools or nice ones. Ask to borrow some tools for the first class or 2 then look online for tool deals. But you'll get a nice 3 or larger dia trunk which is $$$$ train it and take care of it. Don't look into get a pot since you will not have a finish tree at the end of the class you need a year or more to depending how and what branches you need to grow.