When I was doing freelance work, I undersold myself at $75/hr and after six months or so realized that I was on track to make about $30,000 that year. I stopped freelancing and took a salaried position for almost 4x that amount. The problem is, you're doing very well if you can bill 20 hours per week consistently. I had long periods of down time, and I really shouldn't have been charging less than $150/hr if I wanted to make a viable living. I decided I would rather be butt-in-chair five days per week (I still get to work at home) than have several months off per year, but with no money to pay the bills. :)
Edit: if the recipient of $100/hr in TFA is a full time employee, that is indeed a comfortable amount of money to be taking home.
Edit 2: After reading the relevant section, anyone doing this work would be foolish to charge less than $200-300/hr. Given the cost of a rewrite, if you could keep the old systems running for $1M/year, you would be saving the banks buckets of money.
Anyone who thinks that's a lot in the contracting world is undervaluing themselves terribly.