With $1300/month guaranteed income such as social security (i.e. guaranteed income you can prove to the satisfaction of the Costa Rica government) you can become a legal resident in Costa Rica. After a year or two you become a legal permanent resident.
You can maybe live on $1300/mo. if you are willing to take buses and eat on the cheap (i.e. cook beans and rice and local cheap foods) and find very low rent, or better yet, share a place with 1-2 others. The people I know who are living on less than $1500/month are people who own a home or get free rent like for managing an apartment building. (i.e. no rent to pay)
The rules re gringos working in Costa Rica can cause you to get deported if you get caught working. And it does happen.
That said, many many people do work illegally, especially at gringo hotels, bed and breakfasts etc.
If you are willing to risk being deported you could travel around to gringo destinations and inquire about working in a gringo-run hotel or b&b. I once got a free room in a hotel for as long as I wanted in exchange for helping the owner with his computer. This was in the rainy season when the hotel was not at full capacity anyway. If you got a situation like that you'd solve your rent problem and I'm sure you can find someone to teach you the bar tending ropes and bar managing ropes.
So you might find an opportunity like this, especially with your good looks if I may say so. Everyone knows a good looking young girl has more options than an ugly older guy! It's just human nature.
I would say you would have a better chance at an outlying tourist town than in San Jose simply because in San Jose' someone is more likely to see you and complain you are taking a job they feel should go to a Tica or Tico. Of course this could happen anywhere so it is a risk. The people I know who have worked illegally as gringos have done it in out of the way places, not San Jose' or a big town.
If you have money to open a bar, and know how to manage one, you could then legally manage it if you are the owner, as I understand the law. Someone correct me if I'm wrong.
I know people who own their own or owned hotels, or bed and breakfasts, and who do work in them as bar tenders, cooks, desk managers etc. It's illegal technically but they did it for many years and no one ever gave them any problem about it. I think if you own a business and manage it and do hire Ticos to help out, you are less likely to get in trouble for working at your own business. People don't want to see Ticos lose their jobs which is what happens if a gringo owner gets deported.
I am not an attorney and certainly not giving legal advice. Just saying what I have seen and repeating some stuff I've heard. I'm sure someone will correct me if I'm wrong.
Oh, and until you are a legal resident you have to leave the country every 3 months in order to keep your drivers license good. If you don't drive then no problem, you don't have to leave once your residency paperwork is initiated.