I have dreadful trouble trying to find nice work wear in plus sizes - apparently larger ladies don't have office jobs
I know you said jackets aren't necessary, but I just bought a suit online from nextdirect.com, and all up for jacket and pants it was $100. I've only just got it and tried it on, but for the price the quality isn't bad and the sizing is pretty true. They also have quite a few tops and dresses that might be good for work also.
Their AU site (nextdirect.com, need to set your country as AU for sizing and pricing) doesn't really have sales, but I thought that was a good price anyway.
In regards to cardy's -all the ones I have that I wear to work are either from Target or Big W and are normally between $20-35 - Target often have 20% off days, so maybe keep an eye out on their website. I find thy have the best styles suited to work. Some of the other places, city chic for example, are way overpriced on things like that, so I only frequent them at sale time, which is just about over (didn't really notice too many work type things)).
The other places I frequent are online - not sure how you feel about that, but , asos.com and boden.co.uk have nice stuff and have sales on at the moment. Asos also ships free to Australia. Evans and Dorothy Perkins might be worth checking out also.
If you find anything in your travels, let us know!