I like to look nice and am generally pretty well put together - I tend to get a lot of compliments on my sense of style. That said, I don't think you need to dress expensively - if style is important to you, you need to have items in your wardrobe that look nice and fit you well, and that mix and match well with each other so you can create lots of different outfits without getting bored (I realize this isn't a requirement for everyone, but I enjoy fashion).
For example, today I'm wearing a dress I picked up for $5 at Target a couple of years ago (grey/black with a flared silhouette), a purple cardigan I received as a gift, subtle leopard print grey tights I've had for years and dark purple heeled booties I paid $20 for and have also had for years. I wear all of these items of clothing frequently, but in a lot of different combinations and with a lot of other items.
You can have great style without adhering to the trend of the moment, and without owning the brand of the moment.
You also don't have to have great style to be an awesome human being. It doesn't make you a better person or a smarter person, or a more hard-working person. So if it doesn't matter to you, and it's not impeding your life in any way, then who cares. Wear (clean) clothes. Be comfortable. Some of my friends are clotheshorses, and some are not - I hang out with them for their snarky sense of humour and general awesomeness and not because they own $250 jeans.