Glasis, the key to strategic purchasing, really, is doing your homework. This doesn't necessarily mean hiring high-priced experts and asking for special favors from suppliers.
On a smaller basis, think of it as bargain hunting. Know your product well, know exactly how much it costs to produce and gets quotes from various suppliers to cut costs.
These are all things you can do yourself as a small business owner.
Also, once you have established a good relationship with suppliers, they will be more willing to work with you on special order and delivery dates and other cost-saving measures.