Well, from my experience with Harmful Code 1.0, I'm doing about the same damage that an MA does with his special (apart from the uber ones likes Wooden Dummy or FA Redux) for an IS cost that's near nothing (16 for me), while still being able to heal myself (and friendlies) with Restore Group 2.0 running on just about fumes.
Then again, I can only use it once every 8s (I think), but still, I'd imagine a Ballista would be dangerous in IL.
Now, I don't know what a couple of hackers from Vector were using earlier today, but they were throwing Cannons and Bomb/Nukes all over the place and I didn't notice them to stop, I'll have to test with a friend tomorrow about just how many attacks it takes me to burn my IS.
Still, looking at my buffs (I normally go about 40-short on my last one): Evade, Improved Hacking, Resist Combat, Movement 1.0, Gaussian Blur, Determination, Combat Training, and Viral Shielding. That's 410 IS so 370 IS, you toss on my Force Mulitplier's Cost Reduction, after stats comes to 13% comes to a burn of 322 IS.
Looking at that, without an IS Cost Reduction anywhere, you could hit about 24 cycles of Logic Barrage 4.0 and Blast 3.0 without running out of IS.
An interesting note is that they're rather efficient. The efficency (DPS/IS) of the main Ballista moves is 4.85 (Piercing) with Barrage 4.0 and 4.64 with Blast 3.0. With Cannon 2.0 (1.07), Nuke 3.0 (1), and Bomb 2.0 (1.15), your efficiencies approach 1.
(The effeciencies of Barrage 4.0/Blast 3.0 versus those of Nuke 3.0/Bomb 2.0 have about the same difference as those between the Trauma Surgeon heals and the Physician ones. Still, they are about twice as efficient.)
If you look at Karate for example, their effeciencies move between .48 for Wrist Throw (with a Stun chance though) to nearly one with Sidekick Combo (1.12), Maki-Otoshi (1), and EFK (1.15). Not to mention they all require interlock and have 10s re-use timers :o.
Now that's pretty interesting there... and with the short cast times of Barrage and Blast, interuption chance (if they have Concentration at least) has to be rather minimal so...
Also, just because, the effeciencies of the Harmful Codes are:
1.0: .67
2.0: 1.1
3.0: 2.26
With shorter re-use timers then MA moves

.