This is not a good situation, because as an adult, he can refuse treatment up until the point where he is a clear danger to himself or others. This is so incredibly painful for family members, and the frustration is hard to handle while trying to be supportive.
I would gather the family together and sit down to tell him that you love him, you see him hurting, and want to help. Stress
that he does need help, and then transport him to the Emergency Room for an immediate evaluation. He needs to be seen by a psychiatrist before his life unravels anymore. The fact that he stated he wants to die is the ammunition you need. If he refuses to go, you can call the ambulance, and they'll come out. I know this sounds drastic, and it is, but it's done everyday across the country. When a person's brain chemicals are out of order, they do strange things, and need the help of family and friends to do the best for them when they can't do it for themselves.
There are other medications besides Lexapro that are now generic and cost much less. So he can be put on a medication that he can afford, but as long as he is suicidal, I wouldn't give him the full bottle to handle on his own.
You're right on target - this isn't normal at all, and he really needs help.
Please let me know if I can be of further assistance.