I get mine from Target and charity shops. I have plain black trousers from Target (2 pairs) and a couple of tops from Target and 4 shirts from charity shops (charity shops round here often have some quite good name shirts) - I have a jacket from Uniqlo.

In the past 18 months I have probably spent about $140 on work clothes (but I am not fashionable, or have any interest in it really, but I am presentable - I do however normally work in male dominated offices where there is no interest in what you wear). I have found trousers from Target $35 last reasonably well - certainly a year.

I always make do with what I have for first week in office to get the lay of the land - also I do find that offices seem to have terrible temperature control and that what you need to wear doesn't always align with the seasons - so I never go and buy much in one go, just add as I go along - I do find here that often the best item in an Australian summer in the office is a jumper!