How about joining a local dive club? Typically, you'll find helpful, very experienced divers (some actually certed as instructors) who will help you. If you want, you could buy them a beer afterwards.
Pizza works great, too. Excellent point on the dive club. I had a diver tell me I was the first buddy they had they didn't have to pay. Dive clubs can also be a great way to check out local sites and meet other people at different experience levels.
To answer your question about cost it depends on the operation. I worked at shop that paid me to go dive with customers when it was slow. Technically that would be free. Other places we charged $20 to $100 per dive