a horn that goes down to 200 MHz is not available, it costs like 5g. I have horns that can do it (but not in their spec), but I would prefer something inherantly narrow band so you don't get possibly confused by IMD, mixing, gain compression. Always better to have a filter, and the least invasive type of filter is the antenna itself.
And, its light, and cheap, if you make it out of thin sheet metal.
And you can make alot of them and network it to a switching box if you wanna monitor a buncha stuff at the same time. Doing that with regular equipment will drain the bank real fast vs some thing made of sheet metal, a N connector and some metal rod.
I feel like it blows all the options out of the water because of cost, so long you manufacuter it yourself and solder or braze them yourself. Or even rivets for the lower frequencies.
I guess you can make your own horns, but its alot more work,, this consists of 1 piece of sheet metal cut out like a box shape, or 2 pieces if you want to save material
I guess making standard gain horns is an option.. but still for like 400MHz its alot smaller just to have the waveguide section.. if you flare it out its going to be truely massive.