Are there any cheap tools available for printing custom vinyl stickers?
I don't know your definition of cheap, but the Silhouette Cameo vinyl cutter allows you to replace the cutting blade with a colored marker so that instead of cutting the vinyl, you end up drawing on it with computer precision. 

Alternatively, you can feed the vinyl sheets which are made for that cutter through an inkjet to get some image on it and then after it dries, coat it in a light layer of clear coat spray paint to keep it from smearing.