Tall, young guy with average looks, in good shape and introverted. Here's what I would do.
Spend a day just Googling images of different guys. Check out some men's style magazines and sites on Instagram. Take note of the styles you like and download all the photos you like into a folder. As a starting point, musicians and actors tend to have stylists and a lot of money so they dress up well.
Here are a few examples.
Kanye does the rugged rich guy look well:
Johnny Depp if you're the hipster arty guy.
Harry Styles has the young, cool heart throb look that the 18 year olds will love.
Ronaldo is more preppy pretty boy.
Mayweather always looks fresh.
Then I would take the photos you like the best, study them and then go shopping and try to put some outfits together.
With $1,000 you could buy a couple of $200 pillar items, such as a jacket/blazer or sharp pair of shoes, and you could buy 8 or 9 $50-$100 items to give you some variation. Don't waste money on expensive socks or underwear or tank tops. Get all that stuff from budget stores and focus on quality shirts, sunglasses, pants etc.
Remember your style has to be congruent with your personality/lifestyle, so I find it stupid when young guys with no money wear suits or introverted guys try to dress outlandishly. No matter what your personality you can always find a sharp style to suit your game and vibe so focus on that first. You mentioned you have average looks, if that's the case a good wardrobe can definitely elevate your game and knock your looks up 1 or 2 points, especially since you're tall. You'll be surprised how much weight a woman puts on a guy's clothes and what assumptions she makes on him based on his wardrobe.
EDIT: I assumed you were a young guy for some reason, then I noticed you didn't post your age. However any guy can do this, but it's a particularly good exercise for a young guy if you have the money.