ooh, tough one!
I see what you mean about wanting something tailored to 'hold it all together', and on your budget you could have got a suit made, but I think it may now be too late...
A Galaxy-type dress like the grey checked one Jackie linked to may be an option - in fact M&S do a range of 'Magicwear' dresses that are specially designed to, um, hold it all in. I think they're long enough to pass muster, but would need a jacket as they're all short sleeved.
The black crêpe one would be wearable again on all sorts of occasions, and if you could find a jacket with a subtle dark pattern (perhaps something like this or this ) you might be onto a winner. I'd avoid putting anything too colourful over the black dress, but something subtly glamorous like this metallic one might be worth a shot.
Re makeup, I'd steel yourself and go to a department store counter for a consultation to get some tips, even if you don't buy their products.
If you're not used to wearing any makeup at all BeneFit do a very good line in concealing/perfecting stuff that just makes you look better without adding any actual colour - try saying 'I want to look less tired' and see what they do.
If you normally wear makeup but feel stuck in a rut, Bobbi Brown or MAC are good - the line to use here to stop them slamming it on with a trowel is 'I want to look like myself, but prettier'.