My wife will be in La Plata, Argentina for a few weeks. The nature of her visit makes it difficult to know in advance how much local currency she will need and we would like to avoid ATMs. Anyone have experience with sending money via Western Union to Argentina, or alternatives?
The black currency market in Argentina is called the "blue market" or "dolar blue" and is a daily changing situation. An answer here will not serve future readers well; but my answer is a little too long for a comment.
Today, you can check https://twitter.com/dolarblue for the standard but unofficial USD$ to peso rate, and against which any blue trader will trade. Expect to pay a small commission or margin for your transaction.
I can't recommend a vendor on this website. Your best bet for large payments is to negotiate a price in USD; the next best is to exchange for the current blue rate with someone in Argentina that you trust.
The final note to remember is that any Argeninian money you remove from Argentina is worthless. No foreign vendor buys Argentinan pesos.
My personal experience is based on two trips, in July 2015 and in July 2013. Exchanges in Uruguay and in the UK refused to buy pesos. We found timely and accurate cambio information by searching internet forums in Russian.
I have experience, but it probably isn't relevant. When I was there in 2014, the official rate was 8pesos/USD, and unofficially 12pesos/USD. So instead of getting ripped off by the ATMs, I took cash and traded it on the black market. It's not as sketchy as it sounds. There's a main street in the capital where people yell "cambio" and you trade dollars with them. They used to have a pretty slick website and app with charts to track the unofficial price, but now I think only their twitter is still active.
Things are changing, and now that anecdote is irrelevant. But you did ask about my experience. Maybe you are looking for more general advice about getting money in foreign countries?
Usually the exchange rate at foreign ATMs is the same that which the bank gives their customers, and probably the best rate around. There may be an ATM surcharge, but as usual, the machine will tell you when you make the withdrawl. (You should also make sure that your bank won't charge extra for foreign withdrawls. Usually they don't despite their love of hidden fees).
At exchange offices, you will see a worse rate, similar to that from WesterUnion or MoneyGram. With the former, you have to bring cash with you. With the latter, you have to pay an extra fee for the transfer. Pick your poison. Also, MoneyGram is usually cheaper than WesternUnion, but the transfer fees and exchange rates are available on their websites for your research.
TLDR: You probably don't want to avoid ATMs. They are cheapest and most convienent.