1880 would probably make it a Morgan dollar, so the mint mark (assuming that's the marking you meant) is located on the reverse (tails) side, near the bottom, just above the letters "do" in the word "dollar."
If it has no mintmark it means the coin was struck in Philadelphia.
I would pay a dollar for a dollar, after all, it is only a dollar.
See the related link below for a picture of the 1880 silver dollar.
That depends on the denomination of the coin.
Currently a 1880 S Morgan silver dollar in MS65 uncirculated condition is worth $156.
In your search box of your home page type in 1880 silver dollar an click on images. This will bring up many pictures.
1880 is a common date Morgan dollar, circulated examples are $17.00-$26.00 depending on grade.
If you mean a 1880 Carson City Morgan dollar? circulated examples run from $100.00-$300.00
Retail values for circulated coins are $17.00-$28.00 depending on the grade of the coin. 1880 Morgans are a common date.
A 1880-S Morgan Silver Dollar that is in a mint state of MS67 is worth: $ 450.00.
Please see
In MS60 Grade uncirculated, a 1880 S Morgan Silver Dollar is worth about $52. In MS65 Brilliant Uncirculated, it is worth over $330.