I say bullion sites because that's what I have experience with, but I suppose it may hold true with other sites as well. There are different prices for different payment options, with a bank wire typically being the cheapest. My question is would sending the money using Paypal gift pass for a bank wire?
Unlikely. The bank wire is for security, not cost - it's instant and unreversible. Not to mention you have no protection if you use Paypal Gift. They can take your money and run, legally, because you gifted it to them.
That's because their margins are minimal and both Paypal and the CC company charge them for their service. Bank wires don't cost them money. It's not like they'd accept Paypal Gift anyway.
It's kinda scary, actually, how unprotected Paypal Gift is. You could probably say you were duped and successfully dispute a credit card charge, but Paypal wouldn't lift a finger for you. A bank wire is a little more hassle but structurally identical to a Paypal transaction. Just without Paypal to complicate things.