1 Gigawatt * 1 year = 8760 GWh * 0.8 load factor * $0.2 per kWh = $1.35B of only electricity.
They get bulk discounts because their load is 24x7, so the fixed costs covered by a per kWh charge is spread over many more kWh than a residential customer
For DCs doing training, their load is constant as long as training is happening. But as soon as they end a run, their load can disappear quickly. This is actually a problem, as the grid and generators are not designed to see massive amounts of load go away instantly
Several system operators are working on new guidelines about these large loads, and they're working on ways and regulations such that these loads have to ride out grid instability and not just disappear without warning