He released 10 years of tax returns [1], showing modestly high income. His disclosures in Congress - which he would be breaking the law if he lied about, e.g. Trump potential fraud - show higher net with real estate holdings. [2] Still probably 8 digitals starting with a $1 or less.
There are sources that says his father in law is worth $500mm. If you think the father in law will give the couple all his net worth that would put in maybe half way there generously based on that info. But that still doesn't compute with what you said even if misleading. [3] [4]
[1] https://www.texastribune.org/2019/04/15/texas-beto-orourke-2... [2] https://www.opensecrets.org/personal-finances/net-worth?cid=... [3] https://www.politifact.com/factchecks/2019/mar/14/club-growt... [4] https://www.forbes.com/sites/christopherhelman/2018/11/04/is...