I know there is only a very small percentage of people who are looking for a flail mower for their tractor right now, but there was at least one, me lol.
Anyway, Bestco has their 48″ Heavy Duty Flail Mower, model FH-EFGC125 for $1903 on sale for $1174, use coupon " blackweekend" for an additional 15% off Total was $998.21 with free shipping
That's cheaper than there medium and light duty mowers. comes with hammer blades and rated for branches up to 3". Its not a standalone unit, you need a 22hp or greater tractor already.
I chose this over a rotary mower/cutter (bush hog, land pride, countyline etc) due to its size and for my purpose, it should work better for clearing my property of fallen branches, vines and palmettos.
Reviews on amazon and ebay are pretty good, better than other cheap brands like tractor supply county line.