I personally use wipe n spray and it works great. It's not too incredibly expensive
Maybe try using swat. It will help the bite and it repels bugs.
Fly spray and any bites they have I put swat on them. You can get it at any tack store or vet clinic
Banixx and flyspray to prevents more bites and stings
I use honey! It's a Natural anti bacterial and doesn't seem to bother my horse or irritate his skin