If this hasn't been always the case, let's assume that 1.00$ = 5 Francs ...
Here are the price I remember in France (in Nice and Paris) for most video games (the evolution was different for the pinball machines) :
. from 1980 (and perhaps before) to 1982 : 1 Franc = 0.20$ = 1 credit / 5 Francs = 1.00$ = 6 credits . from 1983 to 1985 : 2 x 1 Franc = 0.40$ = 1 credit / 5 Francs = 1.00$ = 3 credits . from 1986 to 1988 : 5 Francs = 1.00$ = 2 credits / 10 Francs = 2.00$ = 5 credits . from 1989 to 1996 : 5 Francs = 1.00$ = 1 credit / 10 Francs = 2.00$ = 3 credits / sometimes 20 Francs (not 2 x 10 Francs !) = 4.00$ = 7 credits
From 1997 to 2000 (I haven't seen arcade places after that), you could buy tokens (their number wasn't always the same depending on where the arcade place was) :