Well, I'm not even seeing a 1.5 Mbps package on their website, but we know it's there, because some people on the forums have it.
For a 1-year agreement, the 3/768 package is:
Free for the first month
$19.95/month for the second and third months
$29.95/month for months 4-12
For a month-to-month agreement:
Free for the first month
$37.95/month every month after that