I think you can use number().
library(scales)
library(dplyr)
#>
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#>
#> filter, lag
#> The following objects are masked from 'package:base':
#>
#> intersect, setdiff, setequal, union
df <- tibble(prem = c(1000.51, 1000.4, 10, 17))
df %>%
mutate(prem_formatted = number(prem, big.mark = ","))
#> # A tibble: 4 x 2
#> prem prem_formatted
#> <dbl> <chr>
#> 1 1001. 1,000.51
#> 2 1000. 1,000.40
#> 3 10 10.00
#> 4 17 17.00
Created on 2020-03-12 by the reprex package (v0.3.0)