My friend doesn't have insurance and looks like his ankle sprained while playing. He hasn't visited
doctor thinking He will not be able to pay the bills. Is there any options? He is having severe pain

Take him to emergency. They will treat them there n bill you later. He can pay later in installment.

Go to emergency and get it over with.

As he is in Visitor visa, Is it better to go back to Nepal for treatment instead of paying thousands of $$ here?

If it's sprained then just lift the leg and make alphabets with the toe in the air, put ice like 4 times a day and take good rest. See videos on youtube. If it's fractured then the pain gets unbearable, just take him to er.

Some bones need to be fixed/placed soon you cant wait till he get back to nepal. So to emergency room asap. Pachi jodiyena bhane jindaki bhar khochaudai hidna parla.

You need to find this guy. He has this special oil, can mend broken legs. Look at this video, he demos breaking a chickens leg and he mends it back with his oil.