Here is equipment catalog of DEC. Mean prices is very approximate. It depends on seller: ebay, USA, England, Russia
equipment catalog
monitors / vt400 family
Model, P/N Item Mean price ~
VT420 ANY COLOR 149 $
VT420-A2 WHITE 120V 149 $
VT420-A4 WHITE 179 $
VT420-A6 WHITE 179 $
VT420-B2 GREEN 149 $
VT420-B4 GREEN 179 $
VT420-C2 AMBER 149 $
VT420-C4 AMBER 179 $
VT420-D6 WHITE 199 $
VT420-D7 WHITE 199 $