He played for the Huddersfield Giants, Canberra Raiders, South Sydney Rabbitohs,[2] the Bradford Bulls and the United States national rugby league team.
A Dubbo junior, Costin made his début for South Sydney Rabbitohs in 1993, before switching to Western Suburbs Magpies for the next season.
[4][5][6] As Super League VI champions, the Bradford Bulls played against 2001 NRL Premiers, the Newcastle Knights in the 2002 World Club Challenge.
Costin played for the Bradford Bulls at centre in their 2002 Super League Grand Final loss against St. Helens.
In the 2003 Super League season, Costin was a nominee for the Man of Steel Award and was the 4th highest try scorer, despite missing the last 5 games through injury.
In 2007 Costin assumed the head coaching role of the Souths Logan Magpies in the Qld Cup before taking charge of the Sunshine Coast Sea Eagles (now Falcons) in 2009, guiding them to a premiership in their inaugural season.