Wedding dress on a budget for someone who sucks at dresses

[BiBiBirdie]

My DH asked me after 21 years, to marry him on Christmas Day. To sum up what a shock it was, I laughed, then asked was he dying of some awful disease I was yet to be made aware of- I had come to terms with us not getting married but most people have called me by his surname for the last 15 years anyway.

Anyway, we are on a budget and I really cannot begin to imagine spending £500+ on a dress for one day.

I'm socially quite awkward too, I don't do dressing up, I live in jeans and Converse. So dresses I am clueless at.
I don't have Mum or Sister or aunts to help out, my mates live 4 to 5 hours drive away so that's not going to be an option. I'm a size 16 (currently cutting back on food and exercising more, doing Dry January and sweet and chocolate free so would hope to be a 14), I have size 38C boobs and a tummy. I'm 5 foot 8. Broad shoulders which puts me off anything strapless.
Can anyone help with styles or where I could find one that won't cost lots? I've looked on eBay and Marketplace/Schpock and Gumtree as I don't mind second hand.
Thanks

I bought a £55 dress from Next, it was white and pretty (and short!) and my whole wedding cost £200 (including registration). Spending thousands on a dress is not something I can get my head around.

I've actually seen some dresses I like on Amazon today. They're not actually wedding dresses, but evening wear, so a bit hybrid. Tempted to buy one as they're around £50 as I can always return if awful.
I know I don't want something akin to a Disney Princess, I'm not for lots of ott lace or bows. I want something that won't be hugely heavy.
Not strapless, and not too tight (tummy being my worst area).
I watched Say Yes to the Dress this weekend and that gave me some ideas.

It was M&S I was measured in. Before my eldest was born and I breastfed, I had a consultation with the local hospital breast specialist, who agreed to use implants to sort them, one was a 34B and one was struggling for an A cup. I was so self conscious of them, I never went to the pool or wore right tops. I was on a waiting list and then found out I was having our daughter.
After her, they grew a great deal, although are a still uneven but you do get better bras now and better padding and I'm so not worried by them.
I do think I may remeasure before trying dresses though or ordering.

M&S are notoriously terrible at measuring.
Try Boob or Bust and/or go to Bravissimo.