Is there a way to turn cellulose into sugar at home?
A method used to break down cellulose into sugars is hydrolysis : 

You could use enzymes to hydrolyze the cellulose to produce glucose, but enzymes cost a lot and as you are looking for a cheap way, using enzymes is not an option. A second method is to use an acid (e.g. sulfuric acid) to produce the glucose (just google "cellulose acid hydrolysis"  and you'll find some useful links)