Bookshelf Speakers with Rel 212se Subwoofer

Wolf von Langa SERENDIPITY.

@grinnell I have a small REL sub with my de Capos, crossover set pretty high. They blend seamlessly. 

Here's my recommendation: Revival Audio Atalante 3 monitors. 

All the best,
Nonoise

A used pair of Joseph Audio Pulsars are well within your budget and are all-around outstanding speakers that’ll let you cross over your sub at a lower frequency than many other monitors.  Fritz speakers also worth a look.  Best of luck.