If you were to make a movie about The Great Depression tomorrow, it would cost you a lot of money to find authentic vintage clothing even if you were portraying a slumworld. It would cost you a lot of money to pay a costume designer to design appropriate authentic peasant clothing if you were to make a movie set in the Middle Ages. But that doesn't mean that the Depression-era poor or Medieval peasants aren't poor people because how much it cost to make their costumes on-screen. If you were to make a movie about Jesus Christ and his Apostles, historically all of whom are supposed to be very poor, the period costumes for Roman-occupied Judea around that time wouldn't come cheap either.
This is a frankly absurd argument, where there's no sense of imagination or proportion being applied to the matter at hand.
The cost of producing a costume for a movie (where costumes are about movement, light, color, fit...about how it looks on camera) has absolutely nothing to do with how expensive or pricey it's supposed to be in-universe for the characters at hand. Especially because in the case of Spider-Man you are dealing with a larger-than-life fantasy character.