I liked Banana Republic Factory when I was first setting up my wardrobe. The online options seem to be limited but the closest store is half an hour away. Depending on how professional you need to dress (business casual vs business professional), TJMaxx/Marshalls can be good for tops (not pants) because those don't necessarily need to be the highest quality (though be mindful of the fabrics). I think not really frequently mentioned but I remember years ago I got my first full suit from JCPenny and I know they have deals.

All in all when I had to wear business professional clothes, I got like 3 pants, 10 tops, a skirt, and a dress + a couple blazers so you can get buy with less (and I find I can generally get cheaper tops vs needed high quality pants because you can always wear a tank top under tops if they're a little sheer due to fabric)

Old Navy is also worth a look for very basic layering pieces and occasionally they have tops that could be work tops.