I'd also go with 215/65R15s. The extra width helps in sand because they float better. That compensates for the tiny loss in ground clearance. 215/70R15 will also fit.
I was in the same boat last year, and ended up getting an aftermarket Plus One set of alloys and 225/60R16 tires, which I love. Mine were $643 delivered, but I got a special on wheels from http://www.discounttiredirect.com/.
They were just $75 per rim, and I sold my steel ones for $100 for the set, so my net cost was just $200 for the upgrade. Totally worth it.