Sparkfun is a distributor, not a manufacturer. They sell modules from several different companies, some good, some bad.
The problem with the 3.3v chips is that the Tx/Rx at the ECM is still 5v. Even if you power it with 3.3v, the signal from the ECM will fry the BT module.
$50 is the average going price. I'll see if I can track down the cheaper ones and post a link.
-Tim