Options from Paris Gare Du Nord to St. Germain & from St Germain to Orly Terminal Sud

From the RER B to Nord it is 1.90 EUR per person, less if you bought a carnet (10-pack of metro tickets) for other journeys in Paris. There are escalators and/or elevators at Nord and St Michel-Notre Dame station.
To Orly, RER B in the opposite direction to Antony, then change to the Orlyval shuttle train to Orly. Cost is in the 7 or 8 EUR per person range. Orlyval shuttle requires a separate ticket.
Now getting to the St Michel-ND station can be done on the Metro with stairs to contend with, or walking. Don't know exactly where you are in St Germain.
A taxi to Orly will be a lot less than $97. No more than 50 EUR. But if you have a lot of luggage, it could be a problem.

Just take a regular taxi for both. The driver's prices are inflated. From Gare du Nord, go to the official taxi line and take a taxi -- expect unless you hit silly traffic to spend about 25 euros. To get to Orly, call Taxi G7 the night before and arrange a taxi for the next day -- dispatch fee will be 7 euros if you call the night before and 4 euros if you call when you call for immediate dispatch and the cost of the taxi will be 30 euros (flat rate from the Left Bank to Orly). Taxi G7 has an English language line. Be sure at Gare du Nord to avoid people who approach you offering a ride and anyone who negotiates a price with you. Have your address written out on a piece of paper (including the postal code) if you do not speak French. Of course, the mass transit suggestions above also work but I think that you may prefer a taxi. The cost for mass transit to Orly from the Left Bank of Paris is is just about the same as taking a dispatched taxi; mass transit on Orly Val is 10.25 euros per person. So unless you have a commitment to mass transit, a taxi makes the most sense for that trip. Depending on where you are in Saint Germain, it may make sense to take the Orly Bus from Denfert-Rochereau (less than 7 euros per person) but that can be a zoo.

Taxis-G7, Reserved Taxi, +330141276699, also has an App for download to request a taxi. Similar to how Uber works.
http://www.taxisg7.com/taxis/commande-taxis