Hi there does anyone know a way of copying an estimate, changing the customer, and keeping the same price rather than resetting the prices?

That really depends on how your pricing is set up.

I am using NetSuite price levels and custom pricing. When the estimate levels are copied the lines with a 'custom' price level remain, however the other lines with set rates get updated

when a line is set to item rate, it has to update the price if the item is updated. it has no reference to an old price and it is not set to look for one.