This isn't quite sunk cost fallacy. This is more common to the behavior (which unfortunately I don't know the name) where people make decisions to save money based more on percentage than absolute total, e.g.being willing to drive from one gas station to another to save a small amount on gas cost but not driving from one store to another to buy an expensive piece of electronics for less when the percentage difference is small even when the total amount difference is high. Does anyone know the name of this bias?
I don't know any name for this, but I like to just refer to it as "thinking logarithmically".
You walk into a store that sells two identical candies. Would you buy the candy that ordinarily costs $2 at 50% off (for one dollar), or the candy that ordinarily costs 10$ for 80% off (for one dollar)?
In an isomorphic situation, sparrows preferred the latter deal.
http://users.ox.ac.uk/~kgroup/publications/pdf/kacelnik_marsh_2002_animbehav_costs.pdf