Most any kitchen scale will do! So long as it can measure in grams. I suggest a digital one.
I find analog scales kind of hard to use when what you're trying to weigh is wiggling around, pretty much negating any superior accuracy they might offer. That's just me though.
I'm blanking on what brand mine is right now, but I got it on Amazon for maybe $30 or so?
Also consider what kind of container you're going to put the pigs in while you weigh them. At the vet they'll sit there in those little shallow bowls out of fear and politeness. At home they'll wriggle right off and away if you don't pen them in!
Get something large enough to hold the pig but that won't block the scale display. A cardboard box with a lid or high sides is a good option.