PERM On Changing Companies

When you change companies, we have to do PERM again so does that mean getting new reference letters from previous manager and professors ? I already got them once for Micro's perm filing. So for people who have changed companies and gone through the PERM process again, how much was it for you all ? Did the new companies accept the old reference letters you used first time ? Just trying to get an idea of how much work I am looking at during this change. TC: 170K