I’ve been using laser decal paper because I never got very good results with inkjet paper. I use Bare Metal clear laser paper. First I make a high resolution master using glossy photo paper in my home printer, an Epson inkjet. Then I take it to Staples and have them run it off on the decal paper. The cost ranges from nothing to about 85 cents, depending on how the copy tech is feeling that day.
This is a useful way of making O-scale decals when all that is available is HO. You scan the HO sheet, resize it and take out the blue background (I use PhotoShop), then print it out and take it to Staples.
You still have the problem of not being able to make white letters. That’s when I turn to Highball Graphics.