How about Detroit? It’s the poster-city for progressive Democrat governance, and it could use the money.
I think that they should just hold it in Washington, DC. It is where most of the delegates live anyway, Congress, Federal appointees, the union headquarters (SEIU, AFSLME, etc.), the liberal media and of course, The One.
They would save a fortune on transportation and hotel costs and be surrounded by people completely unlikely to protest any of their activities.
Perfect!