Many greenhouse kits come with benches and hanging shelves. Other greenhouse manufacturers offer benches and shelving customized to fit their line of greenhouses for an additional cost. In either case, there is a large selection available for any size greenhouse, and it's possible to expand on any shelving that is included with a greenhouse.
Many greenhouse and potting benches will have wheels so you can move them in and out and around your greenhouse, and many will have a small sink for conveniently discarding cuttings and debris as you work. Some are very attractive stained cedar rolling carts with storage space for tools and soil and other planting supplies, in a price range starting at about $150.
Greenhouse benches are priced according to size and material. A 2x2-foot, two-shelf bench made of aluminum will cost about $100, while a 5x10-foot stainless steel greenhouse bench will start at about $1000.
Grow racks and propagating chambers, while not technically 'greenhouse shelving', are very handy and convenient for starting your planting in early spring. They are generally small, enclosed temperature controlled units with multiple sliding shelves that make very efficient use of your greenhouse space, or can be set up outside. A stainless steel propagating chamber with a 22-flat capacity will cost around $1000.
For more information about greenhouse shelving, check out the shopping links at the top of this page.