Have you ever sharpened a knife before?
Do you own any abrasives ( sandpaper , stone )?
What kind of knives do you plan to sharpen, are the sides flat like a kitchen knife or swiss army kinfe, or are the sides angled every which backwards and forwards ("fancy" non-slip joint type folding knife)?
I thought about buying a system, or even expensive stones, but all the knives that survived in my kitchen are under $10 , so I bought a norton economy stone (~$7)
I even thought about making a fancy angle jig, but materials would cost me more than I paid for the stone
if you have a dollar store knife
if you have some sandpaper to glue to a stick,
or if you have a dollar store that sells sharpening stones (lucky)
all you need is a paper wedge angle guide to help you make up your mind
1287394-Sharpening-stone
1282908-freehand-sharpening-help