When I needed professional clothes as I prepared to leave grad school, I used an image consultant. I told her my budget ($1200), that I needed a mix and match wardrobe that would take me through at least a six day conference without significant repetition and that I wanted to be able to wear everything for at least 7-10 years. She booked me in during their annual half-off sale. I went in, tried on a bunch of things she collected for me from their warehouse, and walked out two hours later with a complete wardrobe (two pants, two skirts, three jackets, three shirts, three sweaters) plus a new pair of shoes.
The consultant got paid a commission on everything I bought. I looked up retail costs later and found that I paid way less than it would have cost for me to put it all together myself. (Not that I have the fashion sense to do that anyway.)
That was 3 years ago. I've bought four new shirts/sweaters since then to go with the suits, plus a couple of scarves, but otherwise I already have everything I need. It was a major cost for me, but I saved up for it, and it has proved to be a great long term investment. I still love all of the clothes, and expect to have very few professional clothing costs over the next 7 years. About $120 per year is very reasonable for professional clothes.
Just something to consider if you have the option. It was an amazing experience for me. I am not a big fan of shopping at stores -- I don't mind it for an hour or so, but then I start to feel overwhelmed -- so this was perfect. (Two hours! Full wardrobe! Someone who actually has an eye for these things bringing me clothes! No decisions to make other than, 'do I like this or not?')