In every state it operates, FanDuel's sign-up offer is: Bet $5/day for 5 days, get $50 in bonus bets each day. Promonyx estimates it is worth $175, and it needs about $300 available at once. Use code SJR at sign-up, or the sign-up link on this page.
FanDuel's offer is checked in 26 states: Arkansas, Arizona, Colorado, Connecticut, Washington DC, Iowa, Illinois, Indiana, Kansas, Kentucky, Louisiana, Massachusetts, Maryland, Michigan, Missouri, North Carolina, New Jersey, New York, Ohio, Pennsylvania, Puerto Rico, Tennessee, Virginia, Vermont, West Virginia, Wyoming.
You place one qualifying bet with your own money, and the book credits bonus bets whether that bet wins or loses. A bonus bet pays out only its winnings, never its stake, which is why a bonus bet is worth less than the same amount in cash.
About $175 on $300 of cash needed at once, a 58% return. That is an estimate of the offer before it is placed, based on the book's terms and prices at the time.