It's been posted in almost every thread for the SB6121, but you can get this modem SB6141 from fleabay for $67 with free shipping on a best offer submittal.
Seller is modem-modem. I ordered one about a month ago and it works great.
FYI: If $67 does not work, you cant try $70 - my brother got one for that amount just last week.
i just received mine from that seller for $70. quick shipping too