Honestly i would probably not do custom videos directly, i prefer to use sites for that. some of the best are Customs4u, Youkandy, iWantClips,Manyvids, Extralunchmoney. They all have some sort of escrow system so that when the customers orders his money are put away until you complete the order, that way you know for sure you'll get paid. The sites verify the client themselves but they do take 25-40% of the order value.
If you don't wanna sign up with any of these sites , make sure to take payment before you start working on the video, and that you only accept a payment method that he can't do chargebacks on. Amazon giftcards work well (if you redeem them as soon as you get them) , and i hear other models use Giftrocket or gmail wallet. Those are not available in my country so i can't tell you more about them, but i'm sure you'll find someone here that will. You can send the video to the customer through any filesharing site ( i personally use wetransfer.com) , most of them are free for files under 1 or 2 GB.
As for prices, that totally depends on what kind of video it is and how much work you have to put into it (getting ready, setting up,editing, cleaning up). i've seen models charge between 1 dollar/minute to 10 dollars a minute. I think we all started out pretty cheap only to find in time how much out time is really worth and adjust out prices. Also if the video has resale value (it's a pretty common fetish or doesn't contain his name and co. ) u can make it cheaper but if the customer has a very specific fetish (there's a guy on all the sites asking for a bathtub video with a specific rubber duck that is not even produced anymore) you may want to charge more.
