You are absolutely correct - cost is an important factor.
You mentioned the phrase " noticeable difference". As you may have read here, most changes will be noticeable. That does not mean better or worse, but you will notice the difference.
You have to determine where you want to go, before you randomly upgrade. That can be an expensive journey!
You no doubt have seen many posts for equipment, from many people. There are as many opinions and comments as you want to read. I would suspect that for your budget you could upgrade your system, piece by piece. You can find single disc players of good quality such as Cambridge Audio, Creek, Roksan, Rega - albiet they may stretch you budget for some models. A similar list can be made for amps. I am not familiar with multi disc units, but I am sure they can also be had.
This may sound funny, but why do you feel the need to look for upgrades? Excuse me if I missed this in your posts. Maybe if you can answer what is lacking, you can decide the approach
