Yes, you should go to the ER.
The ER Doctors will only be glad that you can before landing into more complications. At a level of 400-500 you are at high risk of a complication called Diabetic Ketoacidosis, which can render you unconscious and put you in grave danger. You will require insulin infusion, IV fluids and support.
I understand it might be difficult for you to get medical care without insurance. But on the other hand Diabetic related complications can be deadly and can be much bigger financial stress than treatment of Diabetes itself.
As of now there is very little you can do / self treat at home. Please get medical help asap.
Hope this helps
Please feel free to ask a followup question.