Got 5 TTs in two systems. Love them all, but the cheapest is my Denon DP80. Only $600 when I bought mine. Sadly they’ve become more expensive since. Among new TTs, I’d go for the least expensive variant of the Technics 1200G series. IMO that will be superior to any currently available belt drive in the sub $2000 price class.
Beware if the slippery slope. The second system can become an obsession that sucks money. Your Quad 57s are the worthy beginnings of something fantastic.