What are average Costs of emergency room trip?

It really would depend on the nature of the emergency visit. I will give you a few different case scenarios, as this is a really broad question.

Something simple like sutures, or checking a cut for example. These sorts of visits do NOT often require consultations, or other diagnostic tests, so it is usually just the consultation of the doctor this may run about 200$ to 500$

Something that is moderate such as a sprained ankle with a suspected hairline fracture. This requires an extended visit for the ER doc, likely 1 to 2 x-rays, and possibly a few lab tests. With the ER doc, it is charged for the first hour, and then for every half hour after this, the approximate value of this visit would be about $1000=3000. This would be dependant on whether or not a surgeon needs to consult with the patient.

Something serious such as a patient arriving unconscious. This would require a significant amount of the ER docs time, as well as a couple of x-rays, CT scan, possible ultrasound, and then several of blood tests. Depending on what was found during the diagnostic testing, it is highly possible that there will need to be consultation with other doctors, so this would be an expensive visit. The average cost for this would range about $3,000 to 8000 dollars.