You may reach out to a company called Naveris, who has a blood test for post treatment HPV related head and neck cancer patients, if that applies to you. The test is called NavDx and It may be free, regardless of your insurance. But things could change, so I would ask them to explain how the billing works. I think it would have to be prescribed by a doctor, who has supporting information from your treatments.
I have taken the test, and they sent someone to my home to take the sample.

Enlarged left cervical lymph node in neck on 1/9/18. Male, age 60. Had retired from working as a computer technician and a project manager for almost 38 years, on 7/1/17.
Node was removed 1/16/18 and found to have SCC P16.
Chest xray clean.
Since then, PET/CT, slight activity left parotid, possible malignancy left lingual tonsil. MRI clean.
3 endoscopies, nothing seen.
2/26/18 Larryngoscopy,primary not found.
TORS 3/23/18 lingual tonsil biopsy.,biopsy negative.
Chemo/rads started 4/18/18.