Currently using very inexpensive cable, and I'd like to stretch the budget to $750 (or less) and get a cable that will give me more detail, resolution, and soundstage.
Goheelz
Without knowing what you're currently using one can never be sure but I'm fairly confident the Furutech Ag-12 phono cable will provide all the above in spades for around $500 in an RCA-RCA form.
I have this cable (RCA-RCA) between my SUT and phono preamp and was super impressed with the huge improvement over other (non phono dedicated) interconnects I had around - which sounded grainy and opaque by comparison. Beautifully built too.