Bryan,
24 levels is a pretty big rack. It also sounds like you're using a pretty large box. That tends to make racks a bit more expensive to build. See the post from later today about buying vs. building to read more about that.
Think of it this way, it's only about $20 per box.
Now some questions/comments.
>>I used a higher quality vinyl from a sign shop instead of contact paper,
Tell me more about this. Is it sticky-backed? How much did it cost? I may e-mail you about this. I'm VERY interested.
>>... doubled up the reflectix on the back
Oops. Doubling up Reflectix will have little bearing on how well it insulates. This information is on their website. Take a layer off and use it for another project.
>> ... and my figure includes the tubs, heat tape, t-stat.
That's really not bad. In fact, quite good!
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Current snakes:
0.2 Gonyosoma oxycephala - (Silver/Yellow)
3.3 Gonyosoma oxycephala - (Green)
2.1 Gonyosoma janseni - (Black)
3.3 Gonyosoma janseni - (Black & Tan)