I think a much bigger arbitrage opportunity, one that e.g. YC tried to exploit a lot at first, is getting people who aren't looking for money, but would actually be a good investment, to try building a startup. That's why pg wrote so much about why people should build startups - he thought (and I imagine still thinks?) that there are way more good startups that can be built, if only more people were trying to build them.
Drive Capital (ex-Sequoia) is a good example. You might be surprised how uncommon this idea still is today.
If you could buy 10% of a company for $1mm in Chicago and sell that 10% for $1.5mm in SF the next day, that would be a form of arbitrage.
From wikipedia:
> the practice of taking advantage of a price difference between two or more markets: striking a combination of matching deals that capitalize upon the imbalance, the profit being the difference between the market prices. When used by academics, an arbitrage is a (imagined, hypothetical, thought experiment) transaction that involves no negative cash flow at any probabilistic or temporal state and a positive cash flow in at least one state; in simple terms, it is the possibility of a risk-free profit after transaction costs
The way I've seen the word used in startups is more akin to "Tim Ferriss style" geo-arbitrage.