Call it a form of signaling. That is, a method of conveying information between not-trustworthy parties by performing a costly action, where the cost is honestly linked to signaler quality.
In evolutionary biology, this is called the handicap principle. The ability to afford to squander a resource signals biological fitness. For peacocks, a big showy tail is costly and useless, but honestly communicates the peacock’s ability to sustain such a burden.
According to human contract theory, signaling is necessary when there is no other way to believably convey important information. It is a socially-learned strategy, and by definition, horribly inefficient.
In today’s mating ritual, the information being conveyed is “I am genetically fit.” We assume the ability to obtain overpriced food is somehow linked to genetic fitness. It is a costly signal for someone unable to afford food; less costly for someone who can already afford food.
But let’s try to maximize signaling efficiency here. If you want to convey a costly signal to a potential mate, why not just hand over a wad of cash before mating? The informational value of the cash comes from the belief that the ability to accumulate resources is positively correlated with genetic fitness.
There, I just saved everyone a ton of trouble. Happy Valentine’s Day.