"벌" is a noun counter, normally applied to units of clothing (like a suit). Here, a loose translation of the passage : "Of course, it is now out of fashion, but because it is so cheap, with the same amount of money for the (previous) price of a single, new unit, you can (now) buy multiple units." In the above sentence, "벌" refers to the "unit(s)". There are various counters that are more or less shared by Chinese, Korean, and Japanese. They are sometimes based on various categories of objects (books, sheets of paper, etc.), but sometimes they are based on the shape of the objects.

물론 유행이 지났지만 싸니까 신상품 한 벌 살 돈으로 여러 벌을 살 수 있어요. => It's obviously an outdated fashion, but it's cheaper so you can buy several for the cost of one latest product. 벌 is a counting unit most commonly used for (formal) clothing, either single items or coordinated sets. It's also used for kitchen containers and other things coming in sets. E.g: "정장을 두 벌 맞췄다", "주방 용기 세트를 한 벌 새로 샀다", etc.