Well, folks, let's not get too hung on this need to make everything out of Spanish Cedar. A little bit helps with the aroma and that little bit can be supplied by the cigar boxes the cigars come in. And if you take a careful look at many cigar boxes you'll find that they are constructed of a Spanish Cedar veneer plywood...keep that thought in mind.
The important thing to look at in this discussion is the moisture retaining ability of the wood, its dimensional stability in varying conditions of humidity, and this, that, and the other...including the mythical ability of Spanish Cedar oil to kill mold and bacteria...don't hold your breath on that one!
Going back a few hundred years in history we find that cigar humidors were largely constructed of copper or glass because the hide glue technology of time didn't allow for airtight joints in wood under the influence of humidity. (I realize I'm condensing the history considerably, but bear with me). However, clever woodworkers could construct humidors from mahogany available through the Golden Triangle Trade route early in the scheme of things using expertly executed dovetail joints and the like, supplemented with the hide glue. I wouldn't be able to match their work using the tools available to me now so they did a fantastic job at what they did.
Now follow along with me...ordinary mahogany, given its open cell structure, and other other characteristics of the wood, can absorb moisture on the same order as Spanish Cedar and enjoys similar characteristics of dimensional stability. True, it doesn't have that wonderful aroma...but that can be supplied with judicious application of cigar box parts.
DISCLAIMER: Fortunately, I have the machinery which allows me to convert rough sawn Spanish Cedar planks into any form I want. However, if you go looking for prepared lumber or veneered plywood in the usual venues you are going to s**t yourself at the cost!
So, use ordinary Philippine mahogany for the majority of your internal construction needs and reserve the good stuff for flavor!