The 1891 One dollar bill Treasury note has a plain back and is sort of generic. These backs were used because it was thought they would be harder to counterfeit than the fancy backs from 1890. These notes range in values from $75 to $2500 or more in flawless condition. Contact me if you have a note and want value information for it.
The 1891 One dollar bill Silver Certificate is a plainer version of the 1890 Martha. An 1891 one dollar bill is not particularly rare and can be found rather inexpensively. These notes range in values from $75 to $1600 in Uncirculated condition. The notes come with different seal varieties and generally the large brown seals are the most valuable.