Lemi Cell is really good and around 40$ I believe and they are great!
Total saddle fit is one of my favorite half pads. It also works if your horse has high withers like one of my ottbs
I saw Ogilvy, thinline, or a Roma
Lettia, Roma, Total Saddle fit, thinline
I love Dover saddlery there $18 and great quality
Roma half pads are pretty cheap.