Someone like Virgin Mobile sells a portable wifi hotspot, and I imagine most pre-paid phone vendors do as well. Probably cost you in the range of $40 a month for 2.5 to 3 gig, maybe more. I believe there are 3g/4g devices available now so if you have 4g coverage in the areas you will be working it can be very fast.
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I have one of the Virgin Mobile Wifi eggs, it's really good because you don't even have to get it out of your bag or anything. You can USB tether it like a USB modem or use it as a hotspot, depending on how much charge it has etc. The coverage is about as good as the average Virgin or Optus phone coverage (as you'd expect.)
Mine is prepaid but it comes on $29 and up plans. Really awesome.