Deep tanks do indeed take massive amounts of chemicals. You'll never be cost-efficient with one-shot developers in them.
The efficient way of developing in deep tanks is to reuse the developer and replenish it on a regular basis. You mix two liters (or whatever you need) of full-strength developer and use it with several films, making sure you adjust the development time according to the manufacturer's recommendations (with ID-11 I believe it's +10% for each additional film, though I'm not very sure about it). From time to time you remove a little spent developer and replace it with the same amount of replenisher.
I don't know if Ilford offers a replenisher for ID-11, but Kodak does. It's called D-76R (it's different from the developer itself - you shouldn't use D-76 as its own replenisher).

Later edit: I see Ilford offers a replenisher for ID-11, too. Just make sure not to get it mixed up with ID-11 itself. The formula is different. Not by much, but different nevertheless.