(a) The contracting officer shall not execute a contract modification that causes or will cause an increase in funds without having first obtained a certification of fund availability, except for modifications to contracts that—

(1) Are conditioned on availability of funds (see 32.703-2); or

(2) Contain a limitation of cost or funds clause (see 32.704).

(b) The certification required by paragraph (a) above shall be based on the negotiated price, except that modifications executed before agreement on price may be based on the best available estimate of cost.