Subwoofer suggestions for budget system?

My current setup is a pair of Magnepan 1.6 speakers, a pair of Schiit Vidars, Schiit Sol turntable w/Goldring E3 cartridge (I have a VAS-rebuilt Denon DL-103 with Ebony shell and microridge stylus when I can get someone to come set it up for me), Mani 2 phono stage, Asgard 3 headphone amp acting as preamp, Schiit SYS as source selector, Modi 3+ connected to Volumio for streaming digital and an Orchard Audio RCA-to-XLR converter to drive the Vidars in monoblock mode.

I'd like to add a subwoofer to the mix that can keep bass out of the Maggies.  I'd, of course, prefer a dipole sub to go with the dipole speakers, but not terribly picky ATM.  My budget is around $200 to $300 for now.  I have been very tempted to build a pair of my own subs, but that's not in my budget right now.

Suggestions?