There are many online eyeglasses shop that you can go. If you search them in google, you can see many eyeglasses shop are willing provide you prescription glasses at cheap price such as 39dollarglasses, zennioptical.com, lenscrafters.com and firmoo.com etc. I have bought a pair of sunglasses from firmoo.com for their cheap price and nice look, they are worthy the money. Perhaps they can give you good prescription glasses online.
Yes, prescription glasses are available and much cheaper than they were in local eyeglasses shop. And there are many eyeglasses shop online that provide prescription glasses. You can search them from google. Personally, you can have a look at firmoo.com. I have a friend who have bought a pair from them. His eyeglasses are handsome and well made. But they are just a few dollars. You can have a try. Good luck.
There are many online optical stores nowadays such as zenni optical store, glasses usa, warby parker and EyeBuyDirect. They offer different discount and service. You can check them out and find a store which is most suitable for you.