{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/v2/column-formatting.schema.json",
  "elmType": "div",
  "style": {
    "color": "#fff",
    "padding-left": "10px",
    "background-color": "=if(@currentField >= [$ProjectBudget], '#e81123', '#00B294')"
  },
  "children": [
    {
      "elmType": "span",
      "txtContent": "£",
      "style": {
        "display": "inline-block",
        "padding": "0 1px"
      }
    },
    {
      "elmType": "span",
      "txtContent": "@currentField"
    }
  ]
}