A coins value depends upon its condition, mint marks (if any), country of origin, denomination, etc. Your coin is worth between $10 to $28 depending upon its condition, realistically it is worth around $21.
According to the 2010 redbook the 1890-p (no mint mark) is worth VF-20= $22, EF-40= $25, AU-50= $35, MS-60= $40, MS-63= $65, MS-64= $165, MS-65= $1900, and PF-63= $3000
Since it has no mint mark on it, I have to assume that it came out of Philadelphia. Call a coin collector and see what they tell you, you might want to take it in to them. Hope this helps, good luck.
I have the same coin,no mint mark. I am also trying to figure out the value!