Getting there: bus #11 runs from Gare de Saint-Louis, €2.5 (Aug 2018). Taxi from Saint-Louis costs ca. €15-20, and from Basel – €20-25.
A tram line across the border from neighboring Basel opened in December 2017. There are plans to eventually extend the line all the way to the airport.
Buses #603,604,607 run from Basel (from the Schifflände bus stop), €2.8 (Aug 2018). Worth to note, they are labeled with another numbers in France - #3,4,7 (i.e. dropping the leading 60..).
Distribus company operates a dozen of bus routes inside the town. Bus map can be found at Distribus' website, they also suggest to use this lousy trip planner. Single ticket costs €1,70, return €2,80. Crossborder INFLEX ticket to Basel - €2,80 or 3,10 CHF.