I agree that DD has a great build quality. So does Knights Armament, LMT, LWRC, H&K, etc.
I have personally witnessed during courses and training;
DD MK18 shear a bolt lug, LMT gas block come loose and rotate off the gas port, H&K lowers crack between the trigger pins, LWRC full auto guns fail in multiple ways, and a KAC trigger group hammer snap in two.
All theses failures happened around Bushmasters, DPMS, and home built AR's that cost a fraction of the price and performed flawlessly.
Here's my point; price point does not always equal quality.
By all means, treat yo' self and get a true DD MK18; they are great guns. But, building an AR isn't difficult. Or, head online and find the assembled upper that resembles the MK18, and find an assembled lower...attach the two.
I was just looking at Palmetto State Armory (usually a great place for inexpensive yet good parts), and you can build an MK18-like 10.5" pistol for less than $700.