Sirius lifetime subscriptions are available through (at least) 7-31 for $399 payable in four payments (if you wish). You can change radios three times for a $75 fee each time. Some of this info is not on the Sirius website. Call Sirius at 888-534-7474. More info at--
Lifetime sub for $399? - SIRIUS Backstage Forum (http://www.siriusbackstage.com/forum/showthread.php?t=100027)

That's pretty good. I paid $500 for my lifetime. The only thing I'd be worried about is if it will be honored after the merge (if it ever happens).