France - Arrival in Paris - CDG airport to Ecole Militaire metro stop?

We arrive tomorrow (Sunday) morning in Paris, and have to get from the airport to our rented apartment on Rue du Champs de Mars in the 7th.

Can anyone advise what the cost for a taxi will be, roughly? We are a family of four travelling with 1 large suitcase and 2 small carry-on's. We'd like to keep the costs down as much as possible, so we were thinking of taking the RER-metro instead of a taxi. Assuming it is significantly cheaper for us to take the RER-metro, any details on how to do that (including where to buy our tickets) would be appreciated.

Thanks!

With four of you, go for the taxi - will run about 10 euro more than RER/Metro for four but will be loads easier and faster.
Come to think of it, is the RER B line between CDG and town running again? It recently was closed down on weekends for construction...

Thanks for the advice - we took a taxi and it was the right choice. Cost us 57 euros.

Not much time for input on the subject but will note for posterity it's a choice between cost & convenience and travelling alione I chose cost though appreciate it's much different for a family.

I stayed in 7er in May and got from CDG to Gare du Nord and changed to Mtro #4 to Strasbourg Saint Denis and finally on to line 8 direction Ballard to go right to Ecole Militaire. There are other connections but in much busier metro stations like Chatalet so wanted to avoid those and the route I chose worked fairly well.

Thanks for the advice - we took a taxi and it was the right choice. Cost us 57 euros.

Thanks for the update. In your situation I would definitely have opted for a taxi, too. For four people, even with the extra passenger and bag fees, it's reasonably priced and convenient.

Like tcook052, I will also comment for posterity. I live on the border of what I often call "Rick Steves country" in the 7th and when traveling alone from CDG will usually either:

take a taxi if I have a heavy/awkward bag or my bad knee is acting up, or if I'm tired and feel like splurging
take the Air France bus to CDG-Etoile, then the 92 bus toward Ecole Militaire
or
take the Roissybus to Opera and then metro line 8 to Ecole Militaire