my friend got married on a thursday, because it's cheaper dress hire etc, as there's more demand for a saturday.
But depends how cheap you want to go...you can buy a "pre-loved" dress from a charity shop or ebay and get it altered or re-shaped relatively cheaply. They have a wedding selection at BHS and Monsoon.
Obviously keep the number of bridesmaids down - saves on dresses
Photographer...are any of your friends interested in photography? or maybe you could ask at a local photography course to see if anyone is willing, as they all use digital now, you'd only have to pay for what they print - or pay for a disc with all the photos taken and get them printed yourself at e.g. Boots
or get a few disposable cameras and get everyone to take piccies - then get them developed
make your own invitations...if you keep them basic it should be quite cheap and you can get friends to help out making them. or email them
cake - you can buy plain white iced cakes from M&S, then you can decorate it yourself...a few simple cake decorations won't cost much.
ask your friends and family what talents they have that they can contribute - maybe they can help do a buffet? make/decorate the cake?
if you're hiring services try and haggle and see what added extras they can throw in for you...if you don't ask you don't get
or do a runner to Gretna...that'll keep the numbers down and spare you tons of money, and later you can hold a party for friends and family