There are some really good budget templates that you can download online.
I found one on google with an "estimated" and "actual" spend column and then it had sections for like clothing (Bridal Dress, Bridesmaids, Groom, Groomsmen, Accessories etc), Ceremony (Room Hire, Registrar Fees, Giving Notice etc), Reception (Room Hire, Decoration, Favours, Food etc) and then Other (Transport, Rings, Photography etc).
My husband and I sat down before the wedding and filled them in with what we thought we were going to spend - we started with an "in an ideal world" figure, which was shockingly high, so then we worked out what we could live without - what we could get cheaper online etc and gradually got the estimate in line with what we could actually afford. Then, as we were going along we filled in the actual column to see if we'd made savings (or overspent lol).
Like the other ladies have said, EBAY! We found loads of bargains on eBay.