Value of Mexican Peso vs US Dollar in 1920s -- is silver content complete determiner?

I am rewatching The Treasure of the Sierra Madre which is set in Mexico in 1925 and they seem to use the term peso and dollar interchangeably — for example, the trio of prospectors need another 100 bucks in order to launch their expedition and Dobbs wins 200 pesos in a lottery. Clearly the peso at that time was worth much more than its current value vs the dollar but whether it was worth exactly a dollar I can’t find data on for the 1920s.

What I do know is that the peso coin was made of silver (not pure) and I think its total silver content was about half that of a US silver dollar. But I don’t know if silver content completely determined the exchange rate. If it did, maybe Dobbs 200 peso prize was just about exactly what they needed.

Dobbs keeps begging peso coins from the man in the white suit and he can, for example, buy a meal and a pack of cigarettes and still have 20 centavos left over (which is how Dobbs bought the 1/20th of a lottery ticket). I know that depression-era prices were ridiculously low and even 50 cents was more than enough for a meal but 1925 was pre-depression.

We also find out that either 2.5 dollars or pesos was not enough to pay for a single bed in a passable hotel although 50 cents (or was it centavos?) was enough for a bed in the hotel Oso Negro which was full of rats, scorpions and cockroaches. During the depression, the Waldorf Astoria was charging 3 bucks a night for a room so again, the prices of the depression are not a guide.

I suspect the film makers did not worry too much about details like exchange rate.