Maybe your situation is similar to mine. I played in primary school almost 30 years ago, but not in college. My private lessons at the time centered mostly on Baroque style. I had hardly played at all between then and now, so I was "rusty" too, and my primary flute, and open-hole silver DeFord, was also quite "rusty". I got the bug and wanted to upgrade.
I played a few step-up flutes at a local music shop. I'm not really even sure what they were, but there were a dozen on the rack and the shop owner selected a few for me to try. I was not really familiar with the current manufacturers. I was not too impressed with any of them.
I continued to browse the internet, looking for pre-professional models. Eventually, I lucked into finding a local shop which had a couple flutes in stock, and in fact were on clearance. I happened to play a couple Amadeus AF700BOF's and a Jupiter DeMedici. I was attracted to the Amadeus based on the name (made by Haynes) and in this case the clearance price. It seemed to play well, and the headjoint was much more responsive than my DeFord, so it followed me home.
I haven't regretted my purchase, mostly because I seemed to get a really good price, but the flute has disappointed me (or I have disappointed it) in a couple areas. I have not been at all happy with the low register, and between me and the flute I have had intonation difficulties from low to high registers. Also, I find the keys rather noisy.
So what is my point? First, if the flute you have is not playing up to par and needs some work, have it brought back into good playing condition. This will take a chunk of your budget, but the money you spend will add to the flute's value should you sell it. You won't get everything you spend back, but some of it. As an alternative, select a replacement student model, probably new but definitely in good shape and with a good reputation (Yamaha always comes to mind, but there are lots of others that are good).
Then spend a few months practicing daily - longtones, scales, compositions - until you are also brought back into good playing condition. Get yourself an electronic tuner to check your intonation from register to register. I don't recommend concentrating on the tuner while playing compositions - it's counter productive, just let you're ears guide you to the melody.
At that point, you will be in a position to appreciate the differences between flutes. There are places which will ship flutes on trial - search this forum for links - one or two at a time. Spend a few days playing each. You will probably end up paying for shipping, but the opportunity to play the flutes in comparison for a few days will be worth it.
If you check under my user id, you will see that I have posted a number of Telemann Fantasias. I recorded them in order, and it's interesting to listen to the progression as my skills have come back and I have gotten familiar with the new flute. It has taken months, so patience is the key. Enjoy the journey!
Jim