DNA Paternity Test question (Quick and easy solution needed)?

Q: I want to got the cheapest and quickest possible paternity test. This test is for my child’s benefit and does not need to be court admissible.

Additional but unnecessary info:
1. This is consensual with maternal mother.
2. I’m legally adopting irregardless of test results.
3. Child is 2 y/o
4. Am expecting results to confirm I am NOT genetic father.

Additional Details

Maternal mother is my wife
My son came out of her vagina
Only one other possible paternal father who has no interest in being actual father regardless of results.

A: I think they sell them in drugstores like Walgreen‘s now, there’s one called Identigene and a lot of others that are orderable online. The cost of all the home tests I looked at just now is under $80. As far as “quick,” there’s still a several-day turnaround, because the samples naturally have to be sent to a lab.