Can a store raise the price of an item that was already purchased but not yet delivered?

No, a store cannot legally raise the price of an item once you have paid for it. If the store accepted a check, cash, or placed a charge on a customer's credit card, this is considered a completed written contract, regardless of whether the item has been delivered or picked up and whether or not it is actually in the customer's possession.

If a store does not rescind and the issue persists, a customer can send a certified letter explaining that they will bring suit in small claims court. (Click this link for information on small claims courts). If they return the money, as in, fail to deliver the item and instead issue a check for the amount paid, the consumer can sue in small claims court for the difference between the amount of money that was requested from for the item originally and the amount actually paid for the item. 

Benefit of Bargain Entitlement

Consumers are entitled to what is called the benefit of the bargain. This means that if the store breaches the contract by refusing to deliver on their part of the bargain by giving the promised item at the contract price, the court will put the customer in the position the they would have been in had the store honored their promise and delivered the item. Had the store honored the contract, the consumer would have been in possession of an item that, although was originally a smaller price, was actually worth more. Therefore, the court will award the customer the profit they would have made at the time of the exchange. 

To bring the issue to small claims court, check the laws in the state where the incident occurred. There are limits to the amount of money in claims that can be brought in this type of court. Small civil claims are often handled by the individual parties involved, so it will not be necessary, but helpful, to hire an attorney to help with legal documents and court filing deadlines. The main issue at hand is breach of the original contract that was established at the time of the sale; general practice attorneys, as well as most practicing attorneys will have a working knowledge of this area of law and can streamline the process. Consider contacting a professional in your area, and keep in mind that laws vary by state so be sure to understand the laws in your area.