The scales
package provides a few formatting functions,
> scales::percent(c(1.2, 0.13))
[1] "120%" "13%"
> scales::dollar(c(1.2, 0.13))
[1] "$1.20" "$0.13"
> scales::comma(c(1.2, 0.13))
[1] "1.20" "0.13"
> scales::comma(scales::dollar(6000.88))
[1] "$6,000.88"