I'm planning to fly (one-way) from NY to SF. I'm based in Europe and I wonder, will the price (regardless of currency issues) be significantly different if I book it from here, or only when I get to the US? Obviously, I believe its going to be a return flight where I accidentally miss the return part.
It has been proven that websites can do pricing on all kinds of elements (your search history, the browser you're using, your location, your laptop brand, ...) Check this article: lifehacker: how websites vary prices
I don't know if any of the US airlines use this practice. I'm a Platinum FF with AA.com and I always compare the prices they offer on their US site with the prices on their European sites. Sometimes the US site has cheaper prices but more recently is has always been the EU site that showed me the best price. Know however that (in case of AA) the US site requires a US Credit Card to pay for the fare.
I don't know how long upfront you will arrive in the US but I wouldn't push your luck and wait till the last minute to buy your ticket. Maybe your dates are flexible and NY-SF is probably a pretty popular route with a lot of competition (just guessing) but you may end up paying a lot more.
The best time to buy your tickets is not the very last minute but rather on average 8 weeks to 1 month upfront. (Check this article: Best time is 54 days out) I would rather look at this time window than your location.
When travelling domestically I always use the 8-4 weeks time window. For international travel 6-4 months. In my experience we always ended up paying a fair price. To decide what a fair price is I compare with historical and competitors prices.
A LITTLE EXTRA: If you want you can use a browser plugin like Hola. This would allow you to use a US IP address and would simulate that you're based in US. Check the first link in my post for some more tricks.
Also, in this particular case a return might be pricing cheaper than a one-way but it's a myth that this is always the case.
Due to the vast number of sites offering air tickets, mere probability dictates that the answer might be yes for at least a couple of them.
If you want to investigate whether any given site offers different prices to customers depending on which country they are accessing the site from, you can use an Internet proxy to make it seem to the site that you are accessing it from your country of choice. This will allow you to compare various countries.
When using a proxy, you can use the site DNS Leak Test to confirm that the proxy is working as it should be.
The answer to the specific question is no. The price will not change significantly if at all based on where you are physically located.
The price you pay can change based on the local site/currency/credit card you use, but that's due to exchange rates.
Note, for US carriers and domestic routes it is highly unusual to find round trip tickets priced less than one way tickets currently. The 'leisure fare' and 'Saturday night stay' are pretty much gone.