The always insightful Seth Godin suggests that when the customer says "I can't afford it", they really mean is "It's not worth it." He writes, "As in, it's not worth reprioritizing my life, not worth the risk, not worth what I'll have to give up to get this, not worth being in debt for."
A lot of us try to overcome the "can't afford it" objection by lowering the price when, in fact, the fault isn't with the price at all. The fault is our inability to sell the value of our product to the customer. A sales trainer once told me that there are two reasons why a person does something. One is the reason that "sounds good". The other is the real reason. Sometimes the two reasons are the same. Most of the time they're not.
We can drive ourselves crazy trying to close a sale by overcoming the wrong objection. Our job as salespeople is to dig deeply enough to find the real reason why the customer won't buy and then dealing with that objection, not just at the close, but throughout the presentation. In a retail situation, the price of an item should be right there on the sign or tag, visible to the customer from the outset of the conversation. Confirming the fact that the item is something the customer can afford should be done as early as possible, eliminating the "can't afford" objection long before the close.