Jail time for a first time theft in the third degree is unlikely, but a conviction for theft III does carry a maximum penalty of 30 days in jail. $1,250 is the maximum fine for such a conviction. Instead of going to court and pleading no contest, you should speak with an attorney who can advise you of your options, particularly if there is any diversion program in the Court which you are charged (meaning a way to get your charge dismissed through community service, a theft class, etc.). If you cannot afford an attorney, call the Oregon State Bar's Modest Means Program at 503-684-3763, and they can refer you to an attorney. Good Luck, and don't post anymore facts about your case online.
Depending on the store you may be able to go through a "Civil Compromise." In a civil compromise, the defendant compensates the victim for any loss in exchange for an acknowledgment of satisfaction. That acknowledgement gives the court the power to dismiss the charge.
A civil compromise is a great way to get out from under a misdemeanor theft charge with no record but it has to be done right. You'll usually need an attorney to do it because you will probably be ordered by the court not to have contact with the store.
Get an attorney before pleading guilty or no contest and explore your options.
Please don't consider this free information to be legal advice. If you want legal advice, you should retain an attorney.