I buy that concentrate that is sold in TSC for cows/horses. I don't remember if it's pyrethrin or permethrin. And I cover every possible inch that I can. I use a garden sprayer that you pump beforehand and it does not hiss and bother my horses. It gives a finer mist. I use a LOT each time. Thus the concentrate (correctly diluted), though it doesn't have sunscreen or a special scent, works the best for me cost-wise.
For tick repellant, I like EquiSpot (like Frontline for horses), but you should test it in a tiny spot on your horse before you use the whole tube on him. Some horses are sensitive to it and break out in hives. I have used it on five horses and haven't had that problem, but it works very well on ticks. Repeat application every 30 days.
Cost effective fly spray: RepelX concentrate.
Homemade fly spray: 2 cups cider vinegar, 2 cups skin so soft, 1/2 cup citronella oil, a few drops of eucalyptus oil.
I've pretty much given up buying expensive store-bought full-strength fly spray, as nothing seems to last more than 24 hours that I can tell.
We use permethrin in a garden type sprayer. It works for about 20 min if you really soak them in it. That's the best I've found. Fly masks and boots work WAY better, IMO. I haven't tried fly sheets yet.
For ticks, FRONT LINE. Two of the large dog size, one down the mane and withers, one down the butt and dock of the tail. I pick off just a few ticks a week (already dead) as opposed to dozens a week. I've used it on multiple TBs, and none have had a reaction. This was recommended by my vet by the way. I've heard the frontline spray is good too!
Charlie Brown (1994 bay TB X gelding)
White Star (2004 grey TB gelding)