Well, let me rephrase your question back to you.
Assuming WiMax sticks around through December, would you be willing to pay $18 once for 500MB of 4G data every month for the next 20 months? That's less than a buck a month.
I use a Karma wireless hotspot and I can't sing its praises enough. This afternoon, I'm grabbing my laptop and my hotspot and working from the seashore.