I am after a 13-14 inch laptop, I seen the Lenovo Yoga 14" models that sold quickly
I found a Dell Latitude 3379 for $551.20, the main differences look like 13.3" vs 14" screen and the Dell has an older gen i5 5200u vs i5 7200u & i5 6200u in the two Lenovo models, the Dell does have a larger 256GB SSD drive.
I've done some research and it seems there is not huge performance difference between the 5, 6 or 7 gen CPU's, the larger 256GB SSD would be handy.
I've had a look on ebay etc and could not really find anything comparable for similar price, there is a couple on graysonline that I'm watching but it looks like anything with equivalent or better specs will go for significantly higher $.
Main use would be watching videos, running charting software and surfing the net, I do often have many web pages open at once in waterfox.
Apart from the Dell or Lenovo Yoga models if I can find a similar deal, is there any better options up to around ~$600 for a 13-14" laptop?
Your needs don't seems to be very taxing on the processor but if you can, aim for an 8th gen. Leaps and bounds better than previous generations, but obviously costs a bit more.