I've used booking.com for hotels in Argentina, and I was able to pay the hotels directly in cash when checking in (my credit card was only used to guarantee the reservation and was never charged). I bought internal plane tickets in dollars with a US card and found the prices very reasonable (yes, they could have been even lower but the hassle of having someone else buy for you isn't worth it to save $50 per trip in my opinion). I've also bought internal bus tickets in cash pesos directly from Retiro. All this on a tourist visa, of course. On trips outside Argentina (I recommend Chile), you won't have to worry about these silly restrictions.