Many stewartia's available, though pseudocamellia is most common.
Certainly one of my favorite trees.
Nice bloom, beautiful bark, beautiful flowers, which bloom after the spring rush, nice fall color... what more could you want in a tree?
Growin showed you flowers and trunk above.
Here are views of fall color and abundance of flowers, both stewartia pseudocamellia.
Final shot is related tree, stewartia rostrata.
Depends on if the tree is container or b&b (Balled & Burlapped), how tall the tree is and what health it is at. I wouldn't say this tree is common or rare. It is a tree deserving more attention ~ Rolls Royce of trees. Keep that in mind when reviewing it for your garden.
It is not overpriced for retail and the size. I've seen them for less but that was wholesale. Compare this: http://www.hortresource.com/downloads/HORTAvail.pdf w/5-6' @ 240.00. If the nursery who quoted you is good, I'd go for it. Prepare the planting hole correctly.