I bought all my nursing bras at Destination Maternity and I've been fine with them. I had a store credit for Babies R Us and used part of it to purchase a Medela sleeping nursing bra and I like that one too.
I was just at Target last week and bought a nursing sleep tank for around $20-25.
What I also use for daytime at home and nightime are shelf bras.
Btw, don't forget to get the breast pads! My pick is the Nuk Disposable Pads but there are several brands out there. There are also the washable ones too.