When you're talking "quite expensive" for the Silver Puppy or SilverGen it's still a matter of $150-$220 for a lifetime of Colloidal Silver . And I think you get a more uniform, better product in the end.
For example the Silvergen uses regulated voltage so it keeps a constant voltage even as the mix gets more and more conductive as the silver mixes in.
Because of this you get a good batch every time that never yellows with the Silvergen as opposed to just connecting a battery to a couple of silver strips. And just as important or more to a uniform product is an automatic stirrer.
If you're short of cash, you can always get started with a cheap setup - but I'd jump to the Silver Puppy or Silvergen if you can afford it.