yes mr. u r right train is not cheaper everywhere in canada, but when u get ur student card u get find it under ur pocket(much cheaper).
Are u going there only for doing part time job? if ur whole concentration is in part time job only then do one thing go in LinkedIn and find communities like part time jobs in sarnia,sarnia jobs for students etc. and get connect with locals .
dont worry, any active student can get part time job after getting part time work permit, if u think sarnia is this or that for part time jobs, then u can choose other areas to live near sarnia,