My understanding is that you need to do the IR in a helicopter that is valid for IFR operations.
That, with the exception of one jetranger owned by Bristows, means a twin. Elswhere, especially in the US, the restrictions are nowhere near as tough.
As a consequence, an IR in this country is vv expensive, as the twin squirrel is probably the "cheapest". The traditional route was for the North Sea operators to pay for the IR and your conversion in return for a service contract of several years.
Good luck