Standalone 250 GB hard drive for Xbox 360 Slim costs 100 bucks on amazon, so no, I think that a bundle is cheaper that buying stuff piece by piece.
Of course, if you're sure you don't need bigger HDD atm, you can just buy a cheaper SKU and get HDD later.
Back in early 2009 I decided to get 360 Elite, simply because Pro was only a bit cheaper than Elite, and 120 GB HDD costed way more than the price diffirence between models. Since I install every game I own, this space is really useful.








