Thank you for your enquiry. Thyroid nodules are common and more than 90% of the time, they are benign (non-cancerous). If the ultrasound of your thyroid does not have any suspicious features for cancer (e.g. increased internal vascularity, marked hypoechogeneity, microcalcifications, irregular borders etc) and you do not have a family history of thyroid cancer or a history of exposure to radiation, the chances of your thyroid nodule being cancerous will be very low.
Having said that, any thyroid nodule larger than 1-1.5cm should undergo a fine needle aspiration and cytology (FNAC) of the lump (a small needle is inserted into the thyroid lump to extract some cells for analysis in the lab to rule out cancer).
If your lump is palpable (can be felt clearly on physical examination), the FNAC can be done without ultrasound guidance and the charges in a private ENT clinic ranges from SGD 400-800 (including cost of laboratory fees).
If your lump cannot be felt clearly (not clearly palpable, an ultrasound guided FNAC may be required an there may be additional SGD 400-600 on top of the cost of FNAC (hence total cost may range from SGD 800-1400).
Do check out my article on Human on "Doc, I have got thyroid - here's what you need to know" for more info.
Hope this helps and all the best!