I went on their site and made a pre-order. I chose for the price $0.00 (well actually it was in British pounds, but 0 is still 0.) There was some mention of a potential transaction fee. However, I went through the whole process and there was no transaction fee. I completed the pre-order for $0.00. The site even seemed prepared for this and didn't bother asking me for a credit card because the price was $0.00. They did ask for all kinds of other stuff, like street address and mobile phone number. I put in bogus stuff for all that. They wanted an email address, and that's important. They email you the download details on October 10, the release date for In Rainbows.
So basically the price of the whole thing is your email address. Anything else you pay is just your charity to Radiohead. This may seem cynical, but it is reality from an economic standpoint. This is literally Radiohead's proverbial donation hat.
Why then is Radiohead doing this? Well they are selling a "deluxe version" in a fancy box with a vinyl LP of In Rainbows for $82. So they are giving their more devoted fans a chance to blow some serious cash. Otherwise they are clearly using this as a way to generate attendance for a tour, where they will make a lot of money. Presumably they will make more than enough money on the tour to pay for the cost of the infrastructure used to distribute the In Rainbows on the wire.
I don't know of any tour dates being announced yet. So maybe they are just crazy? Yeah, maybe.