It is almost worthless. Its value is 1000 times less than a 500 peso coin produced after 1993 when the Mexican government put out the new peso. so for example if a new 500 peso coin (post 1993) is worth $50.00 the 1983 500 peso would be worth only $0.50.
There was no Mexican coin denominated "500" anything in issued 1967. There was a copper-nickel (not silver) 500 peso coin issued in 1987 - it is worth less than a US dollar in circulated condition, and a bit mor than US$2.00 in Uncirculated condition.
If the coins are dated 1993 or later, 500 pesos would be worth about $50 at current exchange rates. If the coins are dated before 1993, they are so-called "old pesos" worth 1/1000 of current pesos, so they would be worth all of a nickel.
The 100 leones coin from Sierra Leone dated 1996 is worth a US dollar or two in Uncirculated condition. I don't see any 500 leones coin ever having been produced - perhaps you have a token or fantasy piece.