Neighborhoods, USA (NUSA), a non-profit Grassroots organization – Annual National Conference

I need an estimate for hosting a virtual conference expected to have 500 attendees. I prefer a platform that is not listed, so I am open to suggestions. The conference will include various types of sessions such as keynotes, workshops, and panel discussions… (Budget: $750 – $1500 USD, Jobs: Event Management, Project Management, Virtual Assistant, Web Development)