One question about in game currency

Is there a way to make to make a number value equal to a username or the amount of robux something costs on the website?

Not sure what you mean? Please elaborate.

For example a number value is set to a shirts price in robux.
Shirt Price >> 30
Number Value >> 30

Just get the product info’s PriceInRobux: MarketplaceService | Roblox Creator Documentation