That would depend on where you are, which you didn't include in the question.
Asia (Russia) is about 100 miles from the US (Alaska)
East
Probably Asia which is just across the Berring straits from the US state of Alaska.
The USA is located on the North American continent which is joined to the South American. North America and Asia are separated by the Bering Strait.
The US is located on the North American continent which is connected to the South American continent.
Florida is the closest US State and the North American continent is the closest continent.
Asia (Russia) is about 100 miles from the US (Alaska)
East
Probably Asia which is just across the Berring straits from the US state of Alaska.
south america The US is part of North America. The Continent you could say would be closest to North America would be, South America.
Asia http://www.google.com/imgres?imgurl=http://questgarden.com/15/25/7/060131155305/images/k3continents.gif&imgrefurl=http://questgarden.com/15/25/7/060131155305/&h=377&w=500&sz=25&tbnid=vC7bYBgCToAwzM:&tbnh=98&tbnw=130&prev=/images%3Fq%3Dcontinents%2Bof%2Bthe%2Bworld&usg=__xdkqciu0X-X8ohKK3kr1sSd50fw=&ei=jsqlStuxJJKBnQeG--GiBQ&sa=X&oi=image_result&resnum=7&ct=image
The closest place to the southern US border is Mexico, which happens to be in North America, just like the US is. The continent that borders North America is South America.
The Gulf Stream, originating in the Gulf of Mexico, passing the US east coast, crossing the Atlantic in a northwesterly direction is responsible for the temperate climate of coastal northern Europe.
The USA is located on the North American continent which is joined to the South American. North America and Asia are separated by the Bering Strait.
East, would be the closest direction, though it is slightly south, so East by South would be a closer direction.
You cannot put a price on a continent. The closest thing is valuing the gross domestic product of Europe (GDP). Its GDP is about US$18,800,000,000, the largest of any continent.
The United States of America is 9,826,675 km2 in area. The continent closest to being three times this size is Africa, whose area is 30,221,532 km2.