You can order online from B&H or adorama. No tax except shipping charges to other states except NY and NJ. Shipping charges should be cheaper than the tax. Of course, SC depends on the weight, distance and volume of the items. I don't know much about adorama but B&H processing time is very very fast. Ordered some items from them and shipped to Pennsylvania(SC to D.C should not be much different). With UPS 2 days, received them in less than 24 hrs.
If you buy from their stores in NY, 8.7% non-refundable tax applicable. Instant rebates applicable to US addresses. But they don't ship to hotels, motels, inns etc. Not sure how mail-in rebates works...