Would you continue warfarin anticoagulation in patients with unprovoked DVT if switching to low-dose DOAC is cost-prohibitive?  

Would continue warfarin if this is cost-effective and doing well.

If switching to low dose DOAC is an option then could switching to ASA 81 also be an option? If not, I would continue warfarin as long as the patient has been able to maintain a therapeutic INR. I would not lower the INR range.