Alcone sells very inexpensive brushes that I like. alconeco.com Makeup theater brands have their own brushes as well that not very expensive under $15 for most.
Japonesque brushes are now 20-30% off at ulta.com, at great prices. I think it ends in a few days if it hasn't already. They are very very good but a bit expensive at regular price.
Sephora brushes, mainly eyeshadow ones, are now on sale last I checked. Ranging from ~$3-12, usually 7 and up. Type in 'sale' in search box at sephora.com.
Otherwise I would recommend going to an art store and stocking up on some brushes from there, like some smaller filberts etc. I believe many makeup artists pic up brushes this way.
Also on ebay there are some good deals.
Tushka BeLLa I try to wash and care for my makeup brushes like paint brushes. After you are done washing the brushes w/ a cleanser in warm water by making figure 8s in your palm, rinse it all out. Then carefully 'form' the bristles into a shape and let it dry flat. It'll never be like when you first took them out of the package but it will help to retain the shape. Never play with the shape of the bristles when drying, always lay flat.
Sometimes if it came in a package, as long as its clean you can put it back into it. I have a blush brush that came in a stiff plastic 'cone' After its dried, I sometimes put it back into the cone to enforce that shape again.
Also if you want to splurge (and I mean majorly!) there is apparently a $200+ brush from Shu Uemura available from Sephora. I'm not sure how they justify the price.