Unfortunately Oly does not make the DOE Model 633 uppers, only Colt made them (emphasis on made, as they are not in production or their schedule currently). When they were originally released they retailed at $1500, and remained at that price until the ones made of rejected parts were sold for $799 (less bolt) 3-5 years ago. The 633's are one of the most unique and scarce configurations available, and therefore they are not inexpensive (like anything Colt makes is).
Another good example is the Colt Commando uppers with the A-1 contour 11.5" barrel. The complete uppers run around the $1000 mark, from any other mfg you rarely get over the $500 mark.
You gotta pay to ride the prancing pony!