From Krause/Mishler Standard Catalog of World Coins (2004 ed.)
1908 20 francs
6.4516 grams weight
0.9000 gold
.1867 oz of gold

1908 production: 6.721 million (this series has mintage from 1906 to 1914, with annual mintage between 5.3 million and 17.7 million)

For each year, they show:
F - BV
VF - $65
XF - $75
Unc - $115
Value assumptions are based on gold @ $350/oz back in 2003.

Coins of these years have been restruck.

Hope this helps - don't use it in a parking meter.