Who do I hire for gardening/landscaping work?

I just recently moved into my new house, but the yard is a mess. The former owners had a tree grove put in with black plastic wrap underneath some pebble stones. It has been 9 years since someone was living in that house and now it looks like one big garbage bag. Oh and the trees are overgrown and in serious need of pruning. How much is this going to cost me and who should I hire?