It is also likely that you will not be able to find a free paternity test unless you are in a exceptional situation. In this case you would need to get the court and child support services involved. The National Health Service or NHS does not offer free paternity testing. If you require a prenatal paternity test it will not be court admissible due to risks entailed and moreover, fetal DNA extraction and lab analysis for this type of test is very complex which means prices will be very high. Click here for more about prenatal paternity testing.
You cannot forget to also see what the local competition is offering and at what price. A test in the US may be cheaper than one in the UK depending on the extent of competition. Ordering the cheaper test from a company that does not have operations in your country may mean incurring added postage costs and waiting longer for your DNA test results.