Question about cab fare

I can't comment about how the fare compares with a normal taxi from the taxi rank at the station, but my guess is it would be a .lot less then €50, because €50 is the rate from Charles de Gaulle airport, which is many times further.

Yes there is always a public transport, use the métro, which is what you will have to get used to to get around Paris. Whether the métro is suitable depends on whether you can carry your luggage up and down stairs.
The métro costs €1.90 per person. The nearest métro station looks to be Saint-Augustin
A métro map is here: http://www.ratp.fr/informer/picts/plans/pdf/reseaux/metro.pdf
From Gare du Nord, you would have to go south on line 4 to "Strasbourg St-Denis" and then west on line 9 to Saint-Augustin.

Edit: I just checked the distance on a map, it came out at 3.9 Km. This site estimates a taxi fare at €19.20: https://www.taxifarefinder.com/main.php?city=Paris-France&from=Gare+du+Nord%2C+Rue+de+Dunkerque%2C+Paris%2C+France&to=%C3%89glise+Saint-Augustin%2C+Avenue+C%C3%A9sar+Caire%2C+Paris%2C+France&fromCoord=48.8809481,2.3553137000000106&toCoord=48.8762979,2.3188379000000623

We are very comfortable with Paris public transportation, but when we arrive on the Eurostar, we always grab a taxi since we have luggage. It usually is about Euro 20, depending on traffic, from Paris Nord to the 7th arrondissement. It looks like the Metro requires a change of trains, so maybe not so easy with luggage and 4 people, especially if you arrive during the commute.

We've never found the queues to be too long at Paris Nord (Gare du Lyon can be awful), but 4 people might make a difference. There is a price for sanity, assurance of a quality ride, and convenience. That said, Euro 50.00 seems like a lot. I suspect it is Euro 50.00 flat rate no matter what your destination in the city, near or far.

I really don't think of safety being an issue with Paris taxi. Maybe there is something that you are aware of that I am not. But 50 US is high. Even with a lot of luggage two could fit per taxi and still be less totally. 50 is about what we paid when four of us when to the airport.

Thanks everyone. I'm glad I checked with you on the price. I'm going to nix this idea.

, That's 2.9 kilometers or barely over 2 miles. It takes 37 minutes on foot (maps.com) and should be about 10 Euros by taxi(my guesstimate).

note also that there is no extra person charge in a Paris taxi until the 5th person. And at Nord be very sure to only take a cab from the head of the cab line when it is your turn and that the meter is on. This is a hot spot for scammers (although they probably wouldn't charge you more than 50 for that trip) 50 is the cost from CDG to your destination; you are within walking distance. Even with traffic it shouldn't be more than 15 and probably closer to 10.

You could switch to the RER E to St Lazare and take the long underground walk to Eglise St Augustine, but that would be 4 transit tickets at 1.90 EUR each, so a 10 EUR taxi looks like a deal. Even if you have to take 2 taxis due to an excess of luggage, and since safety (not sure about the issue there) is a priority, go with the official taxi line.