It might be a good idea for you to really think about how you want your wardrobe to work for you, rather than buying the odd thing. If your budgets tight, then you are going to need your clothes to work together as much as possible.
There has been lots of talk here about about choosing outfits for 'events' rather than just buying things. So think about where you go and what you want to be wearing. This can be as simple as:
School run
Coffee with friends
Park with DC's
Drink/dinner with DH
think about what you would like to be wearing and try to list an outfit for each. You'll be surprised that many outfits lap over i.e jeans, blazer etc.
Also, when you are in a bit of a rut I think its good to get inspiration from real life people. Keep and eye out when you are out, what women make you think they look well dressed? What is it they are wearing?
In terms of shops on a budget, but that are fashionable, I'd look at:
Zara, New Look, Gap (Good for basic t-shirts, vests) Uniqlo. Often M+S have some very reasonable priced things in their "indigo" range.