When weather is good, this is one of my favorite streets. You can find stores like Burberry, Channel, Armani, etc. The street lies between T Arlington and T Hynes Convention, so just get off the subway and start walking.
The area is very entertaining and fun. Most of the stores are top brands, so it is too expensive to shop, but you can also find not-so-high brands like Gap, Nine West, and so forth, although I barely go inside them. It is not because I only buy stuff in expensive stores, but these stores you can find anywhere.
Because you are shopping on Newberry Street, it won't be too crowded. You shop without hassle, but I do not see many bargains. You would be better off to go the big mall or even outlets for stores like Gap and so forth. I'd rather go to the stores that I cannot find in the mall or anywhere else. Not only can you enjoy the luxury, but you can find quite nice stuff in there. One time I went to a Burberry store when they had a 30 to 40%-off sale, in which I found a very nice leather jacket at a very good price. If you do not find anything in your budget, just enjoy the street, people, and nice cafés.