1960's 4-unit - Need help with doors!

[Brianne Leichliter]

Hello BP fam!

I'm in a pickle trying to replace my entry doors for the apartments in my 4-plex that I bought in August.  The doors that are currently there are original solid core veneer doors.  Over the years, it appears they have been kicked in multiple times, and I repaired all of them so they are usable for the time being and safe for the tenants.  

Here's my dilemma.  The doors are 1-3/8" thick with steel frames.  I quoted commercial steel doors and it was outrageous, both for just the 1-3/8 slab and replacing the frame and all with a 1-3/4" door.

Does anyone have ideas that will be secure for the tenants but upgraded?  I'd like to be able to use the existing metal frames, but I'm not sure where to find 1-3/8" thick doors that aren't interior doors.