Since you need reading glasses and also slightly nearsighted, you may need bifocal glasses to help you get clear glasses. If you don't take ye exam, how can you know your prescription in details. If you have no eye prescription, you probably not get suitable prescription gasses that meet your vision requirements. So, i suggest you visit eye doctor for eye prescription. If you want to save money, you can order eyeglasses from online shop where you likely get it at cheap prices. As far as i know, Firmoo offer glasses in a very low prices. And they also provide free glasses to customers, you can visit their site and have a look.
Since you are nearsighted, you should get a pair of regular glasses for distant vision. I don't understand why you get reading glasses for nearsightedness. reading glasses are designed to help people with close up work like reading and sewing. If you only have problem reading a book without astigmatism and you have the same prescription for both eyes, you can get reading glasses from dollars shop or drug store. The cheap reading glasses from dollars stores won't damage your eyes. I would suggest you have an eye exam because I think you don't need reading glasses but regular glasses for distant vision.
Well, that depends. Sometimes something good also comes out from such dollar stores. They are not really cheap in quality. But you must be more cautious to buy cheap reading glasses, for with cheap price usually comes shoody goods. You'd better buy quality-assured reading glasses even at the cost a higher price.
Reading eyeglasses do not have to be expensive brands. But the cheap reading glasses purchased from dollar stores without prescription can do more harm than good. Cheap reading eyeglasses are not the exact the prescription you need. You may need to open your eyes largely to read with that pair. It will damage your eyes in the second time.