If you had to submit an application for an IDP, can we take it that you are not travelling from North America? Perhaps India?
Your car rental quote is in dollars? What kind of dollars? US dollars?
You will need a Swiss Vignette (toll sticker) to drive on many roads in Switzerland. It will cost CHF40, or slightly less in Euro, needs to be properly affixed to the windscreen, and is valid for a calendar year.
If you use the Eurail pass you should know that for many trains in France you need to buy additional seat reservations (only on regional trains do you not need to do that) and they can be expensive. They vary on type of train and the route and date you are travelling. While an extra cost with a rail pass they are included in the price of a normal ticket, and you can get normal tickets pretty cheaply if you plan well ahead.
But it sounds like you want to be "flexible" so planning ahead to save money wouldn't work in that situation.
There are certain things that you need to know about travelling in Netherlands and Belgium by train, especially if you want the Thalys high speed train. The pass holder reservation fee is very high, nearly as much as a ticket, but planning ahead can save you a lot of money there too. Or you can use a combination of much slower trains and not need to buy a seat reservation.
If you drive, do you know about the speed cameras? And the change from 90 kph to 80 kph on rural French single carriageway roads?
Where are your stays with family? Where in Germany have you got hotel reservations?
If you shared your prospective itinerary we could understand the 5 countries in 2 weeks plan that you have.
Happy travels