@adversamTo continue on rfnoise's promotion of Audio Research, I am going to give my whole story to emphasize how much I love their sound. There are sooo many choices and my experience is very limited, but I am a huge fan and went through this pathway:
Classic 120 mono block amps
LS3B linestage
PH5 phono
CL120s
LS26 linestage
PH7 phono
REF 150 amp
REF 3 linestage
REF 2 phono
GSi75 integrated
The Classic 120s were my first ARC products. I had a B&K preamp and Parasound HCA2200ii amp at the time to compare. Those 110wpc from the ARC sounded much more full and dynamic compared to the Parasound's 250wpc. I picked up a 2nd HCA 2200ii and bridged them so was comparing those 750wpc to the CL120's 110wpc and they CL120s still won. I know it is hard to believe, but they really did! My main point thus far is to not get uber focused on specs. That is one thing I have learned over the years is to only trust your ears. I don't care what the damping factor or rated power is of my ARC amps...they sound amazing and have driven my low to modest efficiency speakers well(86 and 89db)
I accepted that I was a tube fan and sold the Parasound amps and listened to the CL120s for about 3 years before getting the REF 150 along with all the other upgrades you see above. While the REF 150 sounded glorious, I got a GSi75 that popped up for a good price. I thought what the heck, if I don't like it I will resell. Well, I love it and I sold all the separates. They don't pop up too often and that alone would be out of your stated 'amp' budget. The GSi75 has a great phono and DAC so depending on your ability to check one out, you may be able to sell other gear to consider an all-in-one integrated. ARC also has the VSi75 that is a standard integrated with no phono nor DAC. I love ARC's sound and would encourage you to audition. There is rumor of a new integrated in their lineup that is customizable regarding plug-ins like the phono and DAC. This would need time to settle into the used market to be feasible so just an FYI.
While I love my current system I am always curious about other components and lately I have really wanted to hear one of Mark Levinson's latest integrated amps. Their 5805 would be in your budget used and is also an all-in-one with the phono and DAC. Their 585.5 is more powerful and similar to my GSi75 in pricing so would need the selling of your other gear to open up your budget. I have no idea how they sound but have been very well reviewed.
Enjoy the hunt and come back to your thread when you pull the trigger.
Dana