Getting to be that season....!
Cheapest traps I've used are the homemade traps with stinky bait.
Spend a few dollars for attractant and they work great without the smell, so for me (2 horses) it's all in where the trap is going to be cuz I use a LOT of 'em.
I use different sized bottles depending on where I plan to place them (pasture vs cabin) and how often I want to toss or empty 'em. This is a smallish bottle that I would use near my deck...
NOT a salesman for this brand, but the bottle itself is PERFECT for a small trap. If you cut it at the second ring down (under the label) then just barely trim the rounded edge off the top of the taller piece (right side of the first pic), the top inverts and fits snugly inside (second pic), doesnt need tape and makes it easy to empty and re-use if desired. It also has a good indent for rigging a hanger. The disadvantage is that I will have to empty it every couple of days. The advantage is that I can tolerate them nearer the cabin, deck, etc...
Most other bottles need to be taped, hot glued or stapled to keep the two pieces together to prevent (NASTY) spillage. This type is just so messy to dissemble and empty, I just toss when full.
I add several slices of lunch meat or raw chicken, maybe some buttermilk and fill with water to about 2 inches below the opening (where the screw cap used to be).
1 day in the sun and it reeks. 2 days and it's a swamp of black buzzers!
Proper placement can help a lot. Flies are drawn to white and yellow (like the commercial traps), and tho' they are strong fliers, if they're breeding in decaying vegetation, trash cans, manure piles, etc, traps nearby gives them a closer and more attractive meal...
Pest control was part of my job in the Navy, and whenever possible, we were required to use non-toxic control. That being said, I've used fly bait in Cuba and Iraq; just cut holes a few inches up from the bottom of a clear liter jug and it worked GREAT when it was where no one could mess with it! I recommend that the cuts be an inverted V and bent inwards. Flies tend to lift straight up when trying to take off. They fly towards the light and their multifaceted eyes can't figure out the small opening(s).
I also have orchards on two sides of me, so gnats are a HUGE problem. For those guys, I use the smaller trap filled with flat beer or ACV.
One last thought: My experience with chickens is limited, but I would not EVER use a vapor strip (like the old Shell Pest Strip) inside a coop. The vapor is heavier than air and more than one well-meaning parent has almost poisoned their baby hanging one over the crib, so I can't help but think it would be just as serious with chicks. They're getting harder to find, but are still available in some places. Similar in action but not deadly are the sticky traps with attractants. They should be okay if they don't contain dichlorvos (DDVP), but I'd still be very cautious with ANYTHING inside a coop other than tried and true food grade DE... JMHO
Now if I could just kill ALL the ticks BEFORE they mob my dogs!!!