SP List Format Calculated Field

I have a calculated field called Total (data type is Currency) that counts the sum of some columns, formula is below and it works.

=SUM([Aug-22],[Sept-22],[Oct-22])

I want to conditionally format this column so that if the Total is greater than the Budget, add a warning class to the cell. 

The code below i've copied from the MS website. It only works when the column field data type is Number (1, 1.0, 100), it doesn't work when the data type is Currency ($, ¥, €)

When I set the column data type to Currency ($, ¥, €) the column fields are empty, but the css does apply.

How can I apply the formatting to a Currency ($, ¥, €) field?

{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/v2/column-formatting.schema.json",
  "elmType": "div",
  "attributes": {
    "class": "=if(@currentField > [$Budget],'sp-field-severity--warning', '')"
  },
  "children": [
    {
      "elmType": "span",
      "style": {
        "display": "inline-block",
        "padding": "0 4px"
      },
      "attributes": {
        "iconName": "=if(@currentField > [$Budget],'Error', '')"
      }
    },
    {
      "elmType": "span",
      "txtContent": "@currentField"
    }
  ]
}