How much does a D-check cost compared to a new aircraft?
Keep in mind that during a D check, the parts on the plane are already owned. There will of course be a certain amount of parts replaced, but it will be much less than the manufacturer's cost to buy/manufacture all of the parts. There will be thousands of hours of labor, which will be most of the cost of a D check. The cost of maintenance space and taking the plane out of revenue service may also be considered.

According to this financial reference:


  For a 15-year old Boeing 737-300, a D check would likely cost \$1.25-\$1.5 million, representing about 8-10% of the cost of the aircraft.


This book is now 15 years old along with the newest 737-300's, so in today's dollars this would be \$1.73-\$2.08 million, not accounting for changes in the cost of maintenance. Larger aircraft will have larger costs. This seems to put the cost in the same range as other sources.