will they do an MRI of your ankle in the er if you don't have insurance?

An MRI costs thousands of dollars when it's regularly scheduled. I imagine if you went to the ER to get one, they would mark the price up at least 2x that. So you are potentially looking at $4000-8000 .

As an alternative, might I suggest seeing a physical therapist? Their visits cost between $40 and $120 and they can usually identify the location and type of your ankle injury with fairly similar accuracy when compared to an MRI (ottowa ankle rules are 99% accurate in determining whether an ankle injury needs an X-ray). Also, if you get an MRI, once they find out what is wrong they will likely refer you to a PT anyway for treatment and exercises to make it better. So why use the middle man?

Most states have direct access, so you don't even need a referral from a doc. to go see one

Depending on what part of the U. S YOU ARE LIVING IN. In case of a medical emergency your Dr can request that they do one.