we're getting married on a budget too... i have been reading and writing alor of budget weddings bought a brilliant book today on it....
i got my wedding dress on ebay, it is brand new worth a few hunderd and i paid less than £36, my budget for this i had set at £150 because i believed i couldn't get anything cheaper, i have been keeping an eye on freecycle alot of stuff often comes up there from people, but we are going to do simple wedding invitations which able to get loads of card for about £3 then just need to find pack of envelopes which can get from poundland,
hire where u can, mens suits sometimes easier to hire but asda do a great range of wedding stuff!
we're getting our rings from argos but you can get nice ones from james watts. but you can often get both for less than £50 but if you want to spend more go for it.
for photos ask family members if they know someone in family who is great at taking pictures and have them do it as a wedding gift to you? otherwise post on classified you need someone cheap maybe someone who does it as a hobbie or is a student they usually do it for £150 max!
buffet is cheaper than meal, so might be worth putting buffet together yourself, we're hoping to do ours for less than £500....
reg office is good way you can do this for less than £100.
reception venue why not hire a community hall, we're getting ours from 5pm - 1am for £133 + £15 for alcohol licence, we're hiring a bar company who will come free and just keep the money they make for the drinks, going to buy the first round and thats about it, my OH wants alot of bottles of Asti at the wedding as its like or is champange but alot cheaper and tastes pretty good too....
bridesmaids and flowergirls etc you could ask them to buy thier own, or buy on ebay also, lightinabox.com are pretty good for dress prices, or wait till winter sales after wedding season.
wedding cake you can buy the tiers out of Asda, Tesco or M&S and built it yourself pretty cheap...
cars, try and get family and friends to help as much as possible get family member with a nice car to be the main car.....
not sure what else to advice but always here to help and answer any questions. we're doing our wedding on £2k but hoping to do it for less.
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Or you could choose a really small venue so that you have no choice but to limit your guests. They cant argue with you then 
