M&S - you can get 2 for £25 (one white and one black) or you can get nicer lacier ones for a little more but you would have to ask to look in their catalogue unless you have a huge M&S store nearby.
I got fitted and bought 2 nursing bras at about 34 weeks, as I couldn't breathe anymore in the maternity bras I was wearing. However, once DS arrived and the milk settled down I went up one cup size and down one width fitting so had to get more nursing bras anyway.
Like you I also tried Mothercare but they just didn't fit right so I think it depends on the shape of your boobs as to what fits you best.
My advice would be to use your Mothercare bras to start with and fork out most of your cash about 3-4 weeks after you've had your baby when your boob size is a bit more settled and you can try on in different stores.
Like the sound of the bravado ones though