usually between half and two thirds as much as the moneyline, depending on limits. A big road underdog +1.5 used to be the best bets all summer, but sportsbooks aren't as stupid as they were in 2009. Generally road team will cover 30% of all games they lose. Which means the 1.5 is worth a lot more when they have a 75% chance of losing compared to a 50% chance of losing.