There is a great difference, but paying more won't necessarily guarentee you something better.
I look first at how the tube is made. They can be cast or machined; cast with a steel liner; or made from seamless or drawn-over-mandrell (DOM) tubing and welded to the breach plug. Strength is your first consideration.
Next consideration is how it's designed/finished - is it true to a particular model (historically)? Look at quality of finish. Is it so designed as to be useable in re-enactments?
My choices happen to be strong, of such a bore diameter that ammunition is readily available, and I don't care about competing. There are others for whom realism is the most important.