It's a ton - less than the cost of a half decent night out with the missus. I could understand the agonies if it were a grand, but a ton? If you really want to save cash don't buy the mac, buy a PC laptop.
And if you don't think you need the extra 40GB, just wait until you start running out of disc. I long ago chewed up all the disc space on my MacBook Pro and now have to carry external disk drives when I travel with it. I've largely stopped travelling to the US and now only go there when I can't avoid it, but if you'd been caught up in the customs queues behind me while I tried to explain patiently to a trogolodytic official what these external disks were, you wouldn't find it funny.
Faster and more RAM is more important than disk speed - even in heavy read/write operations a decent amount of RAM will buffer the data and you'll not notice the difference in disk speed in normal operation.