So you want to drive a rental car in Europe's "eastern" countries (essentially those that were behind the Iron Curtain until 1989). Since most travelers fly to western Europe, landing in cities like Frankfurt, Munich, Vienna, Paris and Rome, the most common eastern travel scenario is to rent the car somewhere in the west and drive into the east. The most visited countries by car from the west are the Czech Republic, Hungary and Poland. Slovenia and Croatia are also popular. Only the most adventurous head for countries such as Bosnia, Romania, Bulgaria, and Lithuania.

Since rental cars are the least expensive in Germany, it's probably the best place to start when considering an eastern auto tour. Vienna's proximity to several eastern countries, makes it the next-best starting point.

An "Open jaw" itinerary is appealing but expensive. The idea of picking up a car in Munich or Frankfurt and dropping it in Prague or Budapest, then flying home or continuing the trip by rail from there, is a good one but rental companies won't cooperate. Technically, it is possible. The few companies that will allow one-way rentals between eastern and western countries charge substantial drop fees, usually in the $300 to $500 range. That's in addition to the usual rental costs. For some, less-accessible eastern cities than Prague or Budapest, we've seen drop fees quoted of over $2,000.

Auto rental companies aren't keen about letting their cars go east. Unintended "one-way" rentals (the car is stolen) are still a not uncommon occurrence. Thus, rental companies only allow certain car categories and makes into the east. Forget Mercedes, BMW, or Audi. If you're taking a car east, it will likely be an Opel, Ford, or Skoda. You'll also find it difficult to rent an automatic transmission car that's allowed to go east. No matter what kind of car you drive east, make sure you park it overnight in a locked or patrolled garage, and be careful where you park during the day.

Depending on the countries to be visited, there is usually a bit of a premium charged to drive east. A compact car for one week in Germany, including 19% value added tax, is $175. If the same car is to be driven to what most car rental companies refer to as "Zone 1" — Czech Republic, Croatia, Hungary, Poland, Slovakia, and Slovenia—the price rises to $188. The price for a midsize car is $180 without eastern travel and $193 for Zone 1. An intermediate for Zone two—countries such as Romania and Lithuania—is $212. A Zone 1 compact from Vienna is about $342 plus a 72 euro security fee.

Though borders are open these days, and you may not need paperwork to cross them, don't let that tempt you to take a car east without permission of the rental company. To do so would violate the rental contract and thus void all insurance coverage. Check other requirements for driving in eastern countries. Poland, for example, requires an international driver's license. In the Czech Republic you'll need a windshield sticker to drive legally.

If you're getting quotes online at websites such as Expedia, Travelocity, or the rental companies' own websites, don't assume that the prices quoted will allow for east travel. Bottom line is, in almost every case, you'll need the car rental company's written permission to drive into any eastern country, so it's best to pick up the phone and speak to a live reservationist. Of course, the best prices and the most knowledgeable advice on eastern travel by car is at 800-521-6722 or get an online quote here.