There are many variations on blankets according to the climate in which your horse will be. If you are traveling on the A.H.S.A. circuit from Florida to New York (which means that your horse would be clipped in the winter), then I would suggest having a lightweight stable sheet and an antisweat sheet for cool days and a heavyweight blanket and liner, a turnout rug, and a wool cooler for cold days. (If your horse will not be making these types of climate changes, but will remain in a very warm climate, you only need to purchase a lightweight stable blanket and an anti-sweat sheet.)
When the horse is wearing a blanket, if the tips of its ears feel cold, add the blanket liner. Ideally, all of the materials used in the blankets and liners should be breathable, so that the horse won't break out in a sweat. The clothing should fit well so that it stays in place and doesn't chafe the animal; and the turnout rug should have a surcingle and leg straps to keep it from shifting when the horse moves around.
The difference in the cost of blankets usually has to do with durability. There are medium-priced blankets that have the necessary features, but may not hold up as long as the more expensive brands on a horse that tends to tear up blankets. If your horse behaves itself, you might try the following medium-priced combination from Dover Saddlery (1-800-989-1500): Rider's International Stable Blanket (a heavyweight blanket from $69.70 to $78.70, depending on size of horse); Rider's International Lite Stable Blanket (from $54.80 to $56.80 depending on size of horse); Canvas Turnout Rug (the canvas is not breathable, but the wool-blend lining wicks moisture away from the horse--$59.80); Sussex Wool Cooler ($69.70); Cotton Waffle Sheet (an anti-sweat sheet priced at $43.80); Fleece Blanket Liner ($23.80). The "Rambo" line of blankets, which is also carried by Dover, has greater durability, but is considerably more expensive. It may be worth the extra money, however, if your horse tends to tear up everything in sight.