I could not tell as I avoid this airport like hell. There is a bus to Porte Maillot but I believe it is costly (a recent ruling enforced the monopoly). Hiring a taxi should definitively be expensive (as the airport is outside the Île-de-France region).
We've flown once there and we used s private transfer. I can't remember prices as it was a few years ago. We used Ezyshuttle who were excellent. If you look for their web page and send an email they'll reply with a quote.
We have left from there once and decided never more as it was way too far from DLRP and it took about two hours with a mad driver jumping from one lane to anoher beacuse of the traffic
This time Beauvais from Pisa was the only option early in the morning and so we are trying our chance again... we will book RS transport as it is the cheapest option and it is around 70 euros for a shared shuttle for the two of us.