Agree about an attorney drafted letter stating the COA basis as state school avg from two states (or some other reasonable amount the attorney can support from other legal situations with similar circumstances/decrees in your state), and a deadline for getting the forms (FASFA etc) done for current school otherwise will need to take a gap year or receive no money as beyond the legal scope of divorce decree due to non-compliance of custodial parent.
Attorney may say you also have leverage either in or out of your period while you are providing child support.
Use your business brain which will be best for all. Keep us posted on progress. We are rooting for you OP.