If your husband is having type 1 diabetes
where he is dependent on insulin
since his diagnosis, then at least thyroid
test and that too only 'TSH' test is essential as screening. No need of T3,T4,FT3,FT4. In case TSH is in the range of hypthyroidism, then likely that Vit B 12 is on lower side. If the patient is poor and clinically we can make out vit B12 deficiency, we directly supplement them with Vit B12 injections without doing the test. This is harmless. If your doctor has asked to do Vit D test, that is also not compulsory. Make sure your husband is exposed to Sunlight during afternoon hours or get Vit D supplement injection given once in three months if he cannot spend time in the afternoon.
If he has type 2 diabetes, at least once cholesterol test
is essential to decide if he needs treatment for that to avoid future cardiovascular complications. So in short, you can spend say about 500 to 600 rupees and get TSH and Lipid profile
test done from a reliable lab.
I hope this helps you. Take care.