I brought a dress with a plunging neckline, and I can't find a bra for it which is cheap-ish. Where do u recomend I look
My OH says that the wonderbra ultimate plunge would be ideal for this situation, you can get it in nude in case of any peeking too. Its currently £16 at amazon uk and well worth the price as the results are great. If you have firm boobs then she says that you might just want to go bra-less and tit-tape the dress to avoid embaressment. Hope this helps.
I would go the braless and tape it route
xGGx
I agree with GG, it worked for Kyle !
I have a "silicone bra, backless, strapless, nude, self adhesive stick on". Think I paid £1-50 on ebay (from China but they are available from UK sellers). I am a 32DD and it provides (not major) but enough support and they are re-usable. 
x
try figleaves they have some deep plunging bras. x
Thanks for all your suggestions but I found one at asda for £6
I would have said asda, they always have something nice :)