The size of the fish that you are going out for is also going to be a consideration.  If you are going for large fish such as marlin or tuna, then you want to have a large reel that can hold a large amount of strong test line.

The stronger the test, the thicker the line is going to be.  A large reel is going to be necessary to hold enough of this large line to get to the areas that the fish are located at.  If you are only going out for smaller fish, then you do not need to have as large of a reel and the line is not going to need to be as thick as it is going to need to be for larger fish.  If you plan on trying for more than one fish type, then you may want to have more than one rod and reel combination at hand.
 
When purchasing the reel, make sure that it is made for saltwater fishing.  Salt can cause corrosion on some metals.  Look at cars from decades ago that are full of rust; this is typically caused by salting the roads to get rid of ice and snow.  The same thing can happen to reels that are not made specifically for salt water fishing.  The reels that are designed for this purpose are going to hold up longer than those that are made for fresh water fishing.  

A lot of money can be spent on a reel.  It is going to be a waste if it does not hold up to the test of time.  One way you can keep your reel in good condition is by making sure that it is cleaned thoroughly after being used.  Always rinse it off as soon as the fishing is done and when heading back to shore.  Once on shore, wash it more thoroughly with soap and water so the salt does not have a chance to wreak havoc on the reels that were used on the fishing trip.

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