Need to buy a desk chair

Hey guys, I just got a pc a couple of months ago and after some chats with my doctor she's concerned that a lot of the migraines I get are due to bad posture and has suggested I get a better desk chair than the shitty one I've been using for years. I spend a lot of time at my computer and am doing a degree that will keep me at my computer for hours so I wanted to invest in something thats going to last me a while and still be really comfortable. As I am a student however, I can't afford the options out there that are like $1000 and was wondering if anyone had some quality suggestions that are on the cheaper end of the spectrum. Thank you!