Going the Transport Only Route, even with some of the attractive knock down prices available, when considering a used item as a Purchase,
will limit you to the Option of the Built in DAC in the Amp.
Can you find a Standalone Transport used with the Amp’s built in DAC to meet your expectations for a Replay of a Hard Media that you feel assured will meet your expectations of a 'CD Player’ ?
For your Budget to find a Standalone CDT and DAC that will deliver to meet your expectations I feel can be done but will take a time consuming investigation and much luck with finding selected devices at a Purchase Value that will match your Budget Allocation.
For a CDP Only option your choices become quite varied and of many options.
As there are numerous Brands, from different Era’s of Manufacture that can be considered, coupled with different Decoders, DAC Chip Sets and Differing Qualities of Transports.
In the used Market Transport reliability and available replacements and servicing options are often included in the Tick Box for the Purchasing Options.
The Buyer has to express Caveat Emptor when going into this World, and carrying out reliability investigations on any chosen device will be very prudent, and learning of the ease of overcoming anything unforeseen will be time well spent.
It would be a great experience for yourself,
if a attempt was put in place and came to fruition, to loan CDP’s from a Shortlist and trial them in your system.
This will help to give to you a sample of the delivery of a Particular Design and help narrow down the Type of CDP that will offer to you a Playback that will be to your taste, the inbuilt DAC might even offer a surprise as to how it impresses.