You'll need more than 1e300, but not by a lot. Point is, don't get too eager to spend yourself out of e300 territory and accidentally set yourself back days of effort (or more) to get back up there.
The wiki is down and it's been a while since I did my run, but as I recall you'll need about 4e300 when all is said and done. There are a few decos that have a noticeable impact on that bottom line because it's so huge. You might need a little more or less than I did. I don't think there's any possibility that you'd need more than 15e300, even without anything other than computer deco (to enable stocks).
To protect me from myself in the final minutes of my run, I built up past 4e300 and then sank 25% of my funds into the coffee market before I started maxing out the girls. A couple of extra hours trading after committing 500 hours to it is a small insurance premium.