S.C.
YES you can relactate and get him back on the breast. You may not be able to rebuild your supply totally depending on how good it was before, what age he was when you stopped, etc, But you should be able to make it a considerable part of his intake. I wouldn't worry about the taste-- breast milk tastes SO much better than formula!
HOWEVER, I would STRONGLY advise working with a La Leche League leader/group (you can find one here: http://www.llli.org/webus.html) and/or a lactation consultant while you do it. AND be sure you count the wet diapers -- if enough's coming OUT then you know enough is going IN.