Well one 80mm cart for the 3880 is say £40
If you spent £56 on 4 R2000 carts you'd get 68mm of ink [17mm each]
So you get around 12mm extra with the 3880, and save £16 which isn't too bad
As far as I'm aware, the R2000 will use ink for swapping blacks too, same as the R3000 and 3880. It's not that big a deal unless your continuously swapping for matt to gloss paper. I used semi gloss most of the time, so didn't swap too often. I wouldn't worry about the maintenance cart too much, mine never needed swapping out.
There are other advantages to the 3880 too, such as bigger print sizes and grey carts for better black and white prints.
You'll save money, but it's totally dependent on how much you'll be printing.