The PS3 makes the Xbox look like a glorified DVD player with a controller, and with that said, there is a reason why it is now possible for Microsoft to give out free 4GB Xbox's with a purchase of a $700+ Windows computer now.
It looks like in the UK there may be a £20, which is about $30. Maybe there may be a drop to $269.99, but I doubt it. PS3 sales are on the rise right now, and the PS3 is finally profitable, so a price cut may not be so forthcoming.
The PS3 comes with everything you need save an HDMI cable, which you can buy for
less than $3. If you plan on installing games on your hard drive, an upgrade may be necessary.
Fat vs Slim is a preference only, if costs are ignored. I prefer slim as it runs cooler and does not attract fingerprints/scratches/dust the way the fat does.