The ARS price you will see in booking.com is the dollars converted to pesos at the official rate, but if you pay directly to booking, they will still charge you the amount in dollars (more expensive) than paying in Argentina. Another option is check the same places on almundo or despegar, their charge should be processed in pesos in Argentina. Keep in mind the most important part is the POS (Point of Sale), for booking is USA, that's why when you check on booking.com, you may see a 100 dollar hotel, which should show you 36,500 ARS per night (if you select Argentina), but if you prepaid the hotel it will be charged 100 dollars, while a reservation will be 100 dollar but will be converted to ARS when you check in, let say's still the same exchange rate (is locked until December), 36,5k ARS will be less than 40 dollars when you pay in Argentina using your CC.