I'm a 'Brit' traveling to Argentina in a few months, so will be converting Ł to US$ and Argentine Pesos.

We've got a fairly decent airbnb in Buenos Aires, for roughly an Eastern European price.

How expensive is Argentina at the moment for foreigners? Where are the costs comparable to?

Right now, using Dolar Blue, the prices are quite reasonable. In a non-fancy steak place, you can eat well for 2, including decent (but not top end) wine, for under US $50. A short taxi ride home yesterday was about US $2. Many other things are currently quite cheap.

But prognosticating "in a few months" is impossible. If history is any indication, inflation will eat up much of the recent devaluation savings, and then there will be more devaluation. Nevertheless, it is likely that you won't find things very expensive unless you're looking for imported products or eating at the top tourist traps.

The official GBP rate is 78/79 pesos to the Pound

If you do a self transfer to be picked up in person using Azimo or Western Union or similar you would get around 93/94.

And to show you how quick it can change , Western Union is offering 101 this afternoon.

In my opinion if you want quality you'll pay for it. So the exchange rate might not always be as favourable as it seems.

What's best for Argentina, taking USD?

USD $100 bills in excellent condition.

Isnt this the norm... I mean, not just in Argentina. Or am I missing something and in places like Europe, quality stuff is dirt cheap and/or given away....?

Thanks for clarifying.

Twenty years ago the quality of most Argentine produced products from beef to biscuits Ł for Ł or peso for peso was far superior to what is available today.....I've noticed it, my Argentine wife has noticed it as well as most locals I know. I'm in no doubt there is still quality to be had but it's not as widely available as it once was and you to pay a large premium for it.
One example, are you familair with the CARDON brand Alex...the clothing and accessory shops? The quality of their products has dropped dramatically over the years but they still insist on selling them at inflated prices. Similar products to CARDON can be had in Europe for half the price!! There are many other examples.

I should say Argentine produced wine remains the exception in all of this.