Cruises have been a terrific travel bargain the last couple of years. And repositioning cruises offer some of the lowest per-day rates at sea. If you haven't heard about repositioning cruises, they've been around since cruise ships began changing locations with the seasons.

Now that there are dozens of cruise ships in the Mediterranean every summer, there are lots of repositioning cruises in the spring and fall. Around April and May, many ships sail from the Caribbean to the Mediterranean, returning in September or October.

Repositioning cruises are available on cruise ships ranging from budget to five-star plus luxury. So whatever experience you're looking for, you can find it – at a rock-bottom price. In fact, fares for these sailings are often less than $50 per passenger, per day.

In addition to sailing for a song, there are other advantages that might make you want to consider booking a repositioning cruise.

The ships are usually not filled to capacity, which means you'll have an easier time getting appointments for spa treatments, finding a pool-side deck chair, or making reservations for the alternative restaurants. And with fewer passengers in the dining room, the food and service is usually better.

With only one or two port calls, the ships usually arrange special seminars, lectures, or educational programs so there's plenty to do while you're at sea. And most ships have Internet access so you can stay connected with everyone back home.

Of course, all that time at sea is what appeals most to many passengers. Six or seven days with nothing to do but find a deck chair and read a book is a wonderful way to unwind.

Today's cruise ships have all the amenities of a resort on dry land, so you won't have to twiddle your thumbs if you don't want to. From rock-climbing walls and ice skating rinks to glass blowing studios and surf simulators, there's no shortage of activities for young and old. And programs for teens, tweens, and children keep them entertained.

The biggest disadvantage of repositioning cruises is that they don't visit many ports. There are some cruises that make several stops before or after crossing the Atlantic, but compared to a Mediterranean cruise that goes some place new every day, a repositioning cruise is not a good way to see the world.

Of course, you can use the cruise as your transportation and explore Europe on your own after you leave the ship. When the volcanic eruption in Iceland caused the cancellation of many flights, some travelers reached their destination by taking a cruise.

Since you'll be joining the ship in one port and leaving it in another – often a continent away – airfare can be expensive. You might have to purchase a one-way ticket from your home city to Miami and then from a city in Europe back to your town.

If the inconveniences are okay with you, a repositioning cruise can provide a wonderful, affordable vacation that you'll never forget.