The least expensive way to get quality decals is to buy them from one of the many sources on the internet. Do a search on this forum for decals and you will find where to look.

Creating the vector artwork is the easiest and least expensive part of making decals. Printing them on suitable media is the toughest and most expensive part. You need a white underlay or opaque spot color printer. Vinyl decals are generally printed with a printer that can also laser cut the outline. These machines aren't cheap.

Good luck.