So I was in a similar situation about a month back. I find that I spend a lot of time in my home office between gaming and work, I end up going through a chair between 1-2 years (generally closer to one). At work they got us setup with Hermon Miller Aeron chairs, and so I got kind of spoiled as I find they are one of the most comfortable chairs I have ever sat in. I finally decided to just bite the bullet and buy an Aeron chair for my home office. I was able to find the exact one I wanted on Craigslist. It was about a year old (which is really quite new for these chairs) and was in perfect condition. These chairs are comfortable and help you posture. The one at my desk is actually 9 years old and is still in nearly perfect condition after heavy use.
You will end up spending more then you originally wanted (I ended up spending $500), but it is well worth it as it will last a long time.