What is least likely and most likely to do ?

Most Likely to do:

" Try to learn why the customer likes the product, and suggest a similar but less expensive alternative."

This will help you to gain the customer's trust, and will most likely take or buy the alternative if he is convinced of getting the same functionality.

Least Likely to do:

"Offer to check with your Store Manager to see if anything can be done. Ask your Manager how to handle the situation."

This will probably not yield a positive result because the price would not likely be changed, and it may put you in a bad light under your Manager, as he will believe you can't think on your feet or improvise on your own.