Having arrived in the 1st arrondissement walking will most likely suffice for transport. That said, Paris cabs are quite cheap. Still, even they don't have access to much of the carfree eastern end of the arrondissement.
If traveling from east to west by Métro you are probably best off using any other stations than Châtelet/Les Halles unless you have to connect there. Although the Métro trains themselves are fast and frequent, the crowded labyrinth at Châtelet can make getting to the trains an adventure.
