Just a head's up - I tried to renew my P411 account today, and acceptable forms of payment have apparently changed.
The lovely lady in live chat graciously let me know that not all pre-paid credit cards and debit cards can be used. I believe she said the green dot type are still accepted.
You should contact P411 before buying a pre-paid card to use for membership enrollment or renewal to make sure you have the right type.
Side note: any ladies willing to take a Wal-mart pre-paid card in lieu of cash?