In terms of total pay, most travelers make from 100 to 120K per year - up to a around a third of it tax free for qualified travelers that are traveling away from their permanent residence. However, out of this amount, you have to pay for housing (costs of which vary widely based on location and personal preference and are in addition to keeping up your primary residence), health insurance, and get no PTO, holidays, or vacations. It is kind of like working per diem at your existing hospital, more cash in lieu of benefits. With overtime, or working rapid response assignments, or being very choosy, it is certainly possible to make over 200K a year. But a reasonable max might be 150K. Travel assignments to the South or Midwest may pay less than the first range mentioned.
It is tough to pencil out, but anecdotally, when I first started to travel, my hourly was about the same as staff, but instead of saving five percent of my net pay living frugally, I was able to save more like 90 percent. There was just no comparison at all.
However, you should never even consider travel for compensation, you do it first because you love the lifestyle. Staff nurses, depending on where they are, can do just as well as travelers by retirement time, and with a far better lifestyle if they would hate being a gypsy.