Spacers are the cheapest way to go, but you get what you pay for.
adding a spacer on top of the shock extends the entire assembly; making the stock bump stops useless
the bump stops halt compression of the shock, stopping it from bottoming out (becoming completely compressed)- when shocks bottom out the shock body and shock neck take the entire weight of the truck.
Shocks are not designed to take weight directly, only to dampen movement of the springs... So lots of people have broken shocks from using spacers