When I built my studio I was also searching for a solid doors with mass for a double door system at every point of entry.I went to all the big box stores,Home Depot,Lowes,Rona,etc.,but the cost was on average of $800 per door,...and I needed eight doors,...not in the budget to even consider.Then I went to the phonebook for the city I live in and searched for any sort of second hand/bargain business that might exist.That is where I found the door store of my dreams,...a second hand diamond mine called 'St. Pierre Construction'.The business is now based on gutting old hospitals,office buildings,houses,etc,that were going to be renovated so it is easy to imagine that they had just about everything one would need for a studio build.My first walk though I stubled onto hundreds of windows,acoustical panels,glass panes,wood flooring,and yes,even an 8'x8'x8' steel constructed sound proof booth that was used in a hospital when performing hearing tests on patients.
But the kicker was the 4,000 doors that were on display in their warehouse.I came across hundreds of 135 pound wooden hospital doors of varying widths so I bought the 8 I needed for $100 each which included the already installed handle hardware and heavy duty stainless steel 4 inch ball bearing hinges.So I basically purchased all my doors for what it would have cost me for one at a big box store,...which were NOWHERE near the mass of the ones from St. Pierre Construction.
I'm sure there is one of these building demolition businesses in just about any fair sized city.Hope you can find one near you to help save on the expenses.
Here are a couple videos of my build that show some of the items I mentioned above.
Part 1 Sanctuary Studio Control Room Build - YouTube
Part 2 Sanctuary Studio Live Room Build - YouTube