Call reactive function() outside the shiny app

Question

I have created the following reprex which tries to use a reaction function price() outside the shiny app. If i use df<-5 then the code works but when i use df<- price() the code does not work. I have a huge shiny app where i want to source() a huge script outside the shiny app but it takes some input values from a reactive function.

 library(shiny)
    df<-price()
ui <- fluidPage(
    numericInput("price", "Price", value=1, min=1 , max=10)
    ,textOutput("text")
)

server <- function(input, output, session) {
    price <- reactive({as.numeric(input$price)})
    output$text<- renderText(df)
}

shinyApp(ui, server)

I dont want to call the script inside the app because i will have to call it again and again in every sort of output and the script is a simulation which means it changes values each time it is called. I only want to call it once so the values remain the same and i can output them.

---

Trying to use the suggestion by gdevaux. When i try to input the values which come out of a function in a variable it doesnt seem to work. It says 'Error in myfunction(argument1) : object 'argument1' not found '.

library(shiny)

# in script.R
myfunction <- function(argument1){
    return(as.numeric(argument1))
}
f<-myfunction(argument1)  #Trying to put output values in a variable

# in app.R
#source("script.R")
ui <- fluidPage(
    numericInput("price", "Price", value=1, min=1 , max=10)
    ,textOutput("text")
)

server <- function(input, output, session) {
    price <- reactive(myfunction(argument1 = input$price))
    output$text<- renderText(price())
}

shinyApp(ui, server)