Last Sunday in the LA Times, Sony ran an ad supplement that showed their SRP for a 4 GB card from them will be $169 starting August.
Considering how low that is coming direct from Sony I'm confident we can expect to see sub-$100 pricing for third party units a lot sooner than previously expected.
Since the use of PS1 games on the PSP under emulation could be extremely profitable, considering these games had their development cost met years ago and the cost of the bandwidth to send them is measured in pennies, it is in Sony's interest to be sure we have a lot of free space for PSP downloads.