Disconnect the EGR vac line, and put your finger over the little port....with your finger still over the port Reach under the EGR valve and push the Diaphram up...if it dosen't drop down then the EGR valve is A-OK!
Have you checked the EGR solinoid? I had one go bad on my car about a year ago...If I remember it was about $100 or so..
( the EGR sol right next to the Wastegate sol on the driver side valve cover)
If you do need an egr valve. Most of the parts stores have them, auto zone, advance auto, etc. The one for my 84 was about $30.
They'll need to know the number off of the old one to get correct one.