I'd make it more personal and pop in or telephone them directly with an outline of your offer. Just view it as another way to promote yourself. The person you speak to won't be the prize winner but could be another potential client.
It's probably just me (!) but if I'm organising a local charity raffle, I like to make sure that the prizes are something I would be happy to win. If it's a service such as a free facial or cut and colour etc, I'd want to ensure the business owner was competent, qualified and insured at the very least.
(But I am quite fussy about these things as I hate it when people think it's ok to get rid of unwanted crap as raffle prizes)