With the DFRPG's system, it's all about the story of the character. Template are just recipes. Your player can take whatever the story of the character can justify.
For me personally, you could make the character an off-shoot of the Lycanthrope from Fool Moon. That is, a natural channel for a spirit of some kind. In this case, maybe he/she is a channel for some more potent kinds of spirits like a "Spirit of The Slayer". Or maybe a Twin-soul kind of thing.
The above option could be justified in creation by giving the character Demonic Co-Pilot, which I think would make for an interesting take on the "Slayer" concept. Though, it would still be a price.
As others have said, if your player doesn't want to be a changling, vampire or something with a price, a Scion would be your best bet. There are all sorts of supernatural creatures that can reproduce with a human including Bigfoot (See the recent short stories), just pick one. Umbralux's opinions on a new template reflect my thoughts on the most likely alternative if your player wants a wholly "Human" character with some Supernatural help but no price.
Another option would be someone in possession of an Item of Power that gives him/her said abilities. It would be a restriction on the characters abilities in terms of it being able to be taken away but it would get the job done. Or you could say that he/she got an abilities from an Item of Power that he/she isn't in possession of like drinking from the Holy Grail or that kind of thing.
A dark option could be to make someone who has benefited from the research and practices of the Prosthonos Society. It's an organization described in the short story, Backup. Bob describes them as, "Bunch of lunatics in the Baltic Region. They chop off their bits and replace them with grafts from inhuman sources. Vampires, Demons and ghouls and such. Patchwork immortality..." Say the character was in an accident and someone with access to that knowledge rebuilt him/her better, stronger, faster. And you don't even need the slow-mo and the cheesy sound effect.