That depends on which mint. An 1880 Philadelphia (no mint mark) is relatively common with over 12.6 million, as is San Francisco at 8.9 million. The New Orleans is more rare at 5.3 million. The rarest of them all is the 1880 Carson City, which only had a mintage of about 600 thousand.
Currently a 1880 S Morgan silver dollar in MS65 uncirculated condition is worth $156.
1880-series US $2 bills were issued as United States Notes rather than silver certificates. Please see the question "What is the value of an 1880 US 2 dollar bill?" for more information.
Currently as of April 2012 a 1880 Morgan silver dollar in MS63 uncirculated condition is worth around 63 dollars.
Coin dealer, pawn shop, eBay.
Most of them aren't rare. There's more information at the question "What is the value of a 1935 US 1 dollar silver certificate?"
$1,000 silver certificates were only printed in 1878, 1880, and 1891. All are considered to be extremely rare. If you have a bill carrying any of those dates you should have it examined in person by an expert in old US currency to determine whether it is counterfeit.
No simple answer, many US silver dollars are considered rare for different reasons, be more specific and post new question.
Responses to questions on Answers.com are normally specific to one item. Please check for questions "What is the value of an 18xx US silver dollar?", where 18xx is 1880, 1881, etc.
A silver dollar with the national motto E PLURIBUS UNUM on it dated 1880 is actually called a MORGAN dollar, most all US coins have this motto somewhere on the coin. It's a very commoncoin with a retail value of $36.00-$42.00
A high relief 1922 Peace dollar is rare, they have values of $80,000.00 or more.
Your coin is called a Morgan dollar. "American Eagle" coins are modern bullion pieces made since 1986 for collectors and investors; Morgan, Peace, and other standard-issue silver dollars were made for use in ordinary commerce. They were discontinued in 1935. Please see the question "What is the value of an 1880 US silver dollar?" for more information.
Higher-value silver certificates weren't printed very often. The only series dates for $100 silver certificates were 1878, 1880, and 1891.