How can I inspect Scene Render settings in a .blend file from Python externally? I'd like to be able to use an external instance of Python (ie. not Blender's internal python) to read a blend file and inspect it for Render Settings (ie. Start Frame, etc.).

Is this possible without firing up the Blender app itself? I don't want to have to depend on a Blender app, or to import the bpy module because the main project is in Python 2.7.

Also, I'd like to avoid any cli calls to blender to get this information.
While it is possible, using blender will be much easier. A small script that you pass to blender when run from a cli is small and easy to maintain. From another python script you could automate it with -

from subprocess import call
call(['blender','-b','file.blend','-P','script.py'])


You can even have your script generate the small temporary script that gets passed to blender.

However if you really have a need to not require blender to be installed, you may want to look at an old project that appears to have died off called blender-aid, it provided a web interface to blend files and used a python script to access data in the blend file, it was intended to assist project management and allowed file links to be repaired and/or re-factored, so apart from reading a blend file it could also write changes to them. While the full info of reading a blend file is contained within blender's source code, you may be able to get a start with blender-aid's old script here - or at least it will give you an idea of how much code is needed.