There's several on Ebay, Roberts has a couple for 44-45 bucks OBO, free shipping. Just how cheap do you expect ? You should state what you are willing to pay.
In answer to your question, I was expecting to pay about fifty bucks plus shipping from a member. I have bought a number of items by WTB ads where the seller has set the price, and the sellers didn't seem to have any problem with that. My question to you is, do you have an SB 28 available in good working order that you are looking to sell?