Small claims court all the way.
I would also file a complaint with every federal agency you can think of. Oh, I am just *sure* the SEC wants to hear about Prosper again after the latest flap with them. Even Team Obama has some sort of new Consumer Watchdog thingy. Just roll Prosper though the mud.
+1. As usual, Prosper's response is idiotic.
First, did it really not occur to them that many lenders would wind up with less than $25 in their account with no active loans remaining and a desire to not sign new legal agreements?
Second, Prosper has no right to extort your agreement to new and different legal agreements as a condition of returning your money to you.
Third, although it is true that the $25 minimum is a longstanding Prosper policy, the issue here isn't your desire to avoid transferring in to transfer out; it is Prosper's improper attempt to coerce you into agreeing to new legal agreements. There is no longstanding Prosper policy that lenders would be forced to agree to new terms and conditions in order to retrieve their own money. Prosper can simply initiate an inbound transfer for you without your agreeing to the new legal agreements.
Fourth, if there really is a "system limitation" preventing them from allowing you to make an outbound transfer of your entire cash balance, then the obvious solution (to anyone with a brain, which obviously excludes Prosper) is for Prosper to simply immediately mail you a check for your balance.
In short, I believe Prosper's position is so lacking in merit as to border on the patently frivolous. They are moronic for making this an issue -- it just makes them look bad. If it were me, I would send them an email and/or fax stating that if they do not drop their extortionate attempt to coerce you into agreeing to new legal agreements and unconditionally agree to return your money by COB Friday, you will file an action for breach of contract and for conversion in small claims court, and will seek a substantial amount of punitive damages on the conversion claim. I would add that you look forward to hearing Prosper explain to a judge their rationale for withholding your money unless you agree to their desired new legal terms despite your unwillingness to do so. And I would add that once you file the suit, you will not accept Prosper's belated attempt to return your money unless Prosper also pays the filing and service costs of your suit.
I also think a complaint to the SEC and the CA regulators would also be appropriate. Do not, however, use the threat of such complaints in your communication to Prosper in an effort to convince them to return your money. That could constitute extortion.
Of course, as always, TINLA.