All depends on what speakers you're driving.
used Atma-Sphere MA-1 Mk 3(140wpc@8ohms) for ~$7k-$9k or for a little north of $10k used, if you can ever find them, Atma-Sphere MA-2 Mk II (220wpc@2/4/8ohms)
Audio Research Reference 300 MKII monoblocks used ~$10k
Wolcott Presence 220M (220wpc@4ohms) - famous for driving difficult large electrostatic speakers like Soundlabs really well.
used Bat VK-150SE monoblocks ~$9.5k
used Atma-Sphere MA-1 Mk 3(140wpc@8ohms) for ~$7k-$9k or for a little north of $10k used, if you can ever find them, Atma-Sphere MA-2 Mk II (220wpc@2/4/8ohms)
Audio Research Reference 300 MKII monoblocks used ~$10k
Wolcott Presence 220M (220wpc@4ohms) - famous for driving difficult large electrostatic speakers like Soundlabs really well.
used Bat VK-150SE monoblocks ~$9.5k