Hilton Head is great - with all of the separated bike/walking trails. I have only been there once, and we rented bikes from our hotel - so keep that in mind. That particular market might be quite saturated. If you go through with it, check out Sun Crusher bikes. Looks like that model was replaced by the Baja Cruz...anyway, big fat tire cruisers. I heard there was someone up in Charleston that buys a bunch at wholesale every year, rents them out for the summer and then sells them all after the tourist season. So maybe think about doing something similar. The thing with Hilton Head is any business space you buy or rent is going to be incredibly expensive. Something you could think about doing is leading bicycle tours around the island and have bikes for rent for that purpose.