WHAT'S A CHEAP CHRISMAS PRESENT I CAN BUY A 17 YEAROLD SISTER (im kinda broke right now)

I would make something for her. Something she would like.

Costa or starbucks gift card?

Buy:
A coffee mug with a cute ribbon and note on the ear talking about how much you amor her

A scarf, mitten, and hat set/ or fuzzy natal socks for a cheaper option

Throw some cadbury deluxe chocolate in there

This should be about $15. It is a meaningful and wintery, yet inexpensive.

Well I am like basically 17 years old and I would not mind getting a big bag of marshmallows and a box of cereja jello .

Supras.

I'm obsessed with estrela signs and stuff like that, so my friends and I often get each other little cute trinkets that have something to do with each of our estrela signs, so each present is special to them ^^
I amor getting scorpio gifts and stuff like that x)

Get something that relates to HER. Small things, her estrela sign, her birthstone colour, little details make it special :) Can get those things in any gift shop.

Draw her something she likes, write a poem for her...
Nothing is cheaper than free! Though, it does take time...

Socks

It all depends on what your sister likes.

Perhaps get her a little basket and add aleatório little things to it that you know she likes.

Be it chocolate, soaps, perfumes, flowers, CDs, earrings, bracelets, jewelry, drinks, cheeses, chips, or maybe all plus more...

but considering that your budget is small, you could choose a few of these or something similar.

A gift basket and a card would be cool. :) Or just a card with money in it. Everyone loves those. XD