In researching a car rental starting in Budapest and ending in Berlin --- every company charges about $1000 for a one-way rental. Except AutoEurope. They charge $300 (estimated). Do I trust the "estimated" price? What is my recourse if they do not honor the "estimation" and decide to charge me more? Thanks!
I guess I'd contact Auto Europe and get a firm price, not an estimate. They probably have to get it from the car company (given that they are just a broker). Or, just book the car (should be refundable up to a few days before the rental starts) if you don't know the exact car company; then you'll find out and be able to ask the car company directly. If the real price is too high, you can cancel it.
But it's normal for these companies to charge the steep one-way fees for a rental dropped in a different country; you are essentially paying the fee for someone to drive the car back to Budapest.
I'm not sure what your itinerary is, but personally I'd try to do it by train.
I rented through AutoEurope picking up in Madrid and dropping in Lisbon. Instead of using their website, I called their toll-free number and a member of their customer service team researched it and found a rental with Hertz that a substantially lower drop charge than other agencies. I’ve called them often over the years and have found their staff to be knowledgeable and very helpful.