What was said at DDXP was that there wasn't going to be different prices for PDFs based on whether you owned the hardcover books or not. Due to technical limitations, they got rid of the idea of putting codes in the books entirely, so there is no way for them to know if you own the books or not.
Based on that, it SOUNDED like the prices for PDFs would likely be close to or the same as the physical books.
Although the question of whether or not you'd get the character creation rules and the like from the Rules Database wasn't answered directly, based on what was said at DDXP and all of the screenshots I've seen, I'd have to guess no. The rules database APPEARS to be more of a list of feats, classes, powers, paragon paths, skills, magic items, races, monsters, and epic destinies.
My best guess is you may be able to do a search on all the classes in the game, and if you are paying for DDI, then you will be able to click on a class and get the full text of that class and its powers. However, you likely won't be able to search for any of the "inbetween" text. Which means no character creation rules, no combat rules, no leveling information and so on.
It seems to be designed more to be a tool for helping those who already own the books. If, in 2 years from now there are classes in 6 different books, plus magic items in 4 different books, and paragon paths in another couple of books, this will let you easily see a list of them all and browse for the one you'd like to be in a game. You'd still need a PHB to tell you how to roll up stats, how many powers to choose if you're 10th level and so on.