You have two choices with a $500 limit. If you don't mind the effort, a SpinClean and a long read of Neil Antin's pamphlet* will be one way. The second is a vacuum machine that might need to be used to fit in the limit. It will get you 80% of the way to the best any of us can do. An ultrasonic cleaner gets you the rest of the way to what is currently achievable.
This is worthwhile, and likely should come before more esoteric upgrades of cartridge or phono stage in my view. It not only can make an LP as quiet as a CD in many cases, but it will prolong the life of your stylus remarkably.
*the PDF is at this link:
