I got my 3 adult BM's dresses from a bridal shop Romantic of Devon Dresses £159 each + alterations. Glad I did in the end as now have 2 pregenant BM's and the shop have ordered extra material and I have now worries that they won't be able to sort it. Ok will cost extra but proberbly cheaper than having to buy 2 high street dress for each or leaving it ill the last minute. Main reason to start with was because they all have different complexions heights and sizes! Bridal shops gave me more choice on colours once we found the right dress.
Little BM's 2x5yrs and an 8 yrs all off ebay 2011 BHS dresses cost me about a £10 each all brand new. One is too big but looking at getting this altered. If not may start again as they were well under my orginal budget.
Although I think Purple is very in this year so you may be lucky on the hightstreet!