Searching would have revealed lots of info on this topic.

RER train would cost about €9 per pax and take about 40 minutes.

A taxi would cost about €50.

A private van/car from Shuttair would cost €60 for up to 4 pax.

Shuttair is the only Paris shuttle service that hasn't given me trouble like late pickups. See www.shuttair.com/Default.asp?PGFLngID=1 but note that it is prepay via website only. The driver WILL be waiting at CDG with a sign with your name on it. On transit from hotel to CDG, the van came 20 minutes early! Great service, unlike the other shared ride services that I've used in Paris.

For 2 pax, it seems like RER and taxi are the 2 most economical choices unless you want to share a ride in a van, stopping at various other hotels.

However, reading that the arrival is late at night, the RER may not be an appealing choice.

I suggest either Shuttair or printing a copy of the hotel info including name, address, and map to provide the driver. Do NOT use a taxi from a hawker. Use the taxi line if you don't want a ripoff. And agree on a price with the driver, with your printed info, before getting in.

Enjoy Paris! It's great there!!!!