Renting car in Frankfurt returning in Strasbourg

Drop car off in Germany near Strasbourg. Take taxi across border to avoid large drop off fees for a different country.

Is cost prohibitive

Typical drop fee in another country is $500+

What is your definition of 'prohibitive" ?

I would drop in Offenburg and take the train from there to Strasbourg. You can buy a "Europass 24h Family" ticket at Offenburg station for €14.50 for this train ride. That covers 2 adults (+ 2 kids under 15 if you have any of those.)

It's a walkable distance between the Offenburg rail station and the Offenburg Europcar outlet (one of Autoeurope's cooperating agencies.)

But satisfy your curiosity and get a quote. You don't know unless you ask.

There are a few rental agencies by Offenburg station with a train almost every 30 minutes into Strasbourg and they take 30 minutes, costing 10 EUR.

hey hey beverly
big drop off fee from one country to another!!!!! get a quote and if outta your range how much between one city in germany to another city in germany. drop off near train station and cross the border on train and reserve another car.
up to you to decide what is important and cost effective. no one can decide for you, it's all about you
aloha

Just a guess, but I'm wondering if the reason you want to drop a car and then go to Strasbourg is that you want to take the train to Paris. If so, when looking for your Strasbourg to Paris train, see where it stops in Germany before going to Strasbourg. Most Paris bound trains in Strasbourg are coming from Stuttgart by way of Karlsruhe, where they also stop, so you could drop the car in Karlsruhe and take the train from there to Paris. I see at least one TGV coming from Freiburg that stops at Offenburg before going on to Strasbourg. Russ covered the Offenburg option in his post, but didn't mention that a train to Paris stopped in Offenburg.

Connecting with a Paris-bound train in Karlsruhe or Offenburg would avoid having to take another train to Strasbourg.