It is the bases and shades that make the money, burners are dime a dozen and chimneys are still being made.
Victorian bases fetch the best money. Good shades are like gold dust, I used to be able to sell the better ones for upto 2 or 300 pounds in the 1980's. Victorian Bases would sell between 50 and 150. Never found a complete one. There was not much of a market for 20th century ones back then.