Here's my 382 cents... Since I work at a bank/credit card call center. We don't have daily outside customer traffic, but we do get groups of corporate visitors that are potential customers for whom we are asked to observe "business casual" dress for since we are allowed to wear jeans every day ( I am tryin' real hard not to go totally off on what some people pass off as dressing up as far as the phone unit is concerned -- read: hookers)
So, I used to be able to wear a denim skirt but they deamed that was a no no. So, I have a khaki skirt and a black one. I wear that with a washable suede jacket and a shell underneath. I also have worn a black jersey knit lower shin length tank dress that has a short sleaved buttoned jacket, the length of which falls just at the waist. They don't allow bare arms, and frankly, I wouldn't show mine at work if you paid me! I have some basic flats I wear since we are up and down walking around and such and as far as I am concerned, heels are for weddings, funerals, and prom. I guess i do have some short heels that I would consider for "business dress." That term, then, is interpreted at our place as men should wear suit, dress shirt, and tie, and women wear a suit/skirt-jacket. And of course, proper hosery.
I'd say do a nice blouse and trousers for day, and jazz it up for evening with a jacket and add a tish more accessory and a skirt for evening. If you shop, perhaps you'd be lucky to find a jacket, pant, skirt combo to invest in... then compliment it with different shells or casual pants which can be found pretty economically
Hope that helps! I know what it's like trying to dress right for work and for weather! Nothing worse that wearing something to a fancy occasion only to feel like you have on a tissuepaper outfit when you dash from car to building...