Okaayyy, so Rhino is weird, I had to change the first line to

var sublistId = String("price" + CURRENCY_ID);

and now it works, what gives!?? headbang

I have encountered other times the Rhino interpretter failed to consider the result of string concatenation as a string (even when all operands are strings). E.g. building search filters for search.create

var filterExpr = [
    "formulanumeric: case when regexp_like({memo}, '(^|\\W)" + dynamicValue + "(\\W|$)') then 1 else 0 end",
    "equalto",
    "1"
  ];

SSS_INVALID_SRCH_FILTER_EXPR_TYPE: Malformed search filter expression, first two elements must be strings.

Workaround was the same.