Art follows Sarah to Felix's loft and takes the cash out of her trunk in episode 1x01 "Natural Selection". From episode 1x03 "Variation Under Nature". From episode 2x05 "Ipsa Scientia Potestas Est". Appears in 2 more episodes.
Source: Orphan Black — Wikia
From episode 2x06 "It's Better to Burn Out Than Fae Away".