I understand better than anyone when it comes to the struggle of finding both affordable and form-fitting business attire. I struggle more than most due to my size and height, so I am always on the prowl for places with a large range of options. Many of the stores mentioned below offer a nice selection of sizes, colors, styles, and fits. Some are online stores and some are physical locations. Moreover, some may carry a little of everything or some may only carry certain items.
While I never fit any of T.J. Maxx's pants, I do love their selection of tops! Better yet, many of their tops may seem too casual for business attire but when paired with the right slacks and the right blazer, it might just do the job!
Some may disagree with me but in my opinion, Marshalls is very similar to T.J. Maxx. Marshalls is always one of my favorite stores to check out, not just for business attire but also for casual clothing and even shoes! I always find a couple of blouses here and there that work and all for a great price. I have gotten many blouses here for under $20, so this is one of my go-to stores.
Loft Outlet is another favorite of mine. They are always having crazy sales. With this store, you know you are getting quality material. Some of the items I've purchased used to be $90+ but at the Outlet, I have gotten them for around $30. My favorite part about this store that many others don't have is their range in sizing. I shop in their petite section for pants and blouses, it's such a life saver, especially when you factor in that I'm a 4'11, 90 pound gal.
Everybody loves Target. They have a pretty large selection of clothing, a good portion of which happens to be business attire. Their sizing isn't my favorite but I have found some pretty decent blouses there!
H&M is where the majority of where I purchases my blouses. I personally prefer plain tops, either solid colors or a very simple pattern. H&M has pretty much everything I need and better yet, they carry blazers, blouses, and slacks!
Forever 21 is honestly hit or miss. If I thoroughly thumb through their selections, odds are I will find one or two blouses that will do the job.
Plato's Closet is a good option if you don't mind buying used clothing. I know some people are iffy about germs and prefer to buy new clothing, but if you don't mind, they often always have a couple of workable options.
Nordstrom Rack is a great option due to the fact that you know it will be great quality. The only issue might be that it is still somewhat pricey, depending on the brand and the featured sale, but sometimes paying a little extra for top-notch quality is worth it.