Our response is provided based solely on the information provided in your question and we strongly recommend you check with your local contracting organization and legal office concerning the specifics of your question.
As you are apparently aware, FAR 15.408 requires contractors to submit their modification proposals in Table 15-2 III.B format when certified cost or pricing data are required. The table instructions for column 2, "Estimated cost of all deleted work", requires the contractor to use "current estimates of what the cost would have been to complete the deleted work not yet performed (not the original proposal estimates)." If a quote that was originally obtained is still valid, it is a "current estimate." If it is not, a current estimate should be obtained.