Perfect Big Sur Area (CA) place to camp?

Okay well this Summer my family and I (2 adults 5 children) would like to go camping. We were thinking of somewhere beautiful, river or ocean side, and fun. I wanted to go to Big Sur, but about 98% of the tent sites were booked.. so where can I find somewhere to camp with my family.. in a beautiful forest or by a river or ocean in early July.. that won't cost me an arm and a leg? Thanks.