- Less than $2 for 1" size on Amazon - 
- Menards has these furniture grade corners - 
- Formufit - PVC corner construction set - PVC 101
- How-To Manuals - PVC Field Manuals freely sourced by FORMUFIT for cutting, cleaning, assembling, bending, sizing.
- Plans and Design Ideas - http://www.formufit.com/free-pvc-projects-plans/
- Goes up to 2" size - $5 -