Go to any skate shop and buy a roll of deck tape. Usually between free and $5. One sheet will do over a dozen handguns.
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I have used Talon Grips and they were nice and worked great. They are cut for the shape of the gun.
The sandpaper grips will tear up a shirt. I had it on my duty gun and it put holes in my uniform shirts. Probably wouldn't be that comfortable if you carried IWB. There was also the same grips but with a rubbery material that worked good and didn't tear up clothing.
MOTOR51
A silicon carbide treatment is definitely the best option. I don't know about Glockworx, but the companies that I'm familiar with offer a wide variety of grits for a wide variety of hands.
I'd consider stippling as well, though in my experience, it's not quite as effective as the aforementioned option (or even skate tape) with sweaty/oily palms.
There's anti-skid tape designed for stairs and metal surfaces that often get slippery, which is notably more aggressive but less "abrasive" as skate tape. I've never used it personally, but I'd assume it's better for a carry gun than skate tape-- in terms of marking up your clothing. I've shot guns so fitted, and it's my very favorite stick-on option to date.
Then again... My hands are covered in calluses already, so it might not work for everyone.