If I let my car go in chapter 7 .can I go get another car with a cheaper payment before inmeet with the trusttee

You should contact your attorney.  If your case is alraedy filed, in most cases, a debtor should not purchase any property, including a vehicle, until the trustee has reviewed the case and issued a Notice of No Assets in the case.  In most cases, debtors will not be able to bet financing from a lender until they have their discharge.   If you have not filed yet, you definitely need to speak with your attorney before puchasing.  Purchase of a new vehicle could cause a delay in when you are able to file by up to 6 months.