I used to work in the industry. Before I did I planned my own traditional white wedding for much less than friends marrying at the same time.
Church
My family church where I was confirmed basic costs, organ player
Registry offices are often gorgeous now and CDs/mp3 can be just as good.
On the friends and families theme, a friend of mine had a very famous singer as a nephew who sang at her wedding. But most of us have someone talented in our circle.
Dress - ex display 10th of full cost, nobody would have known. Ex display, buying from independant retailers, from high Street stores, not having a 'wedding' dress all bring costs down.
Also shop at the right time. December and January are quieter for wedding retailers but also march/April as they're getting rid of last year's stock to make room for this year's, wedding season is Easter onwards.
Shoes - non wedding shoes just pale colour
Flowers - local florist very helpful, also help from family with one particular flower.
Cake - local baker, simple design, 2 tiers only and I still had cake coming out my ears (200 at wedding).
Engagement and wedding rings - h Samuel, not because they were cheap but they had the designs we liked. Several friends have made their own from various heirloom items.
Stationery - local word of mouth I found a guy who was just starting out and doing it as a cottage industry. I negotiated a discount by allowing him to put name of business and number in very small lettering on back of order of service, they were so gorgeous some of my friends still have them (20 years later!) This was pre Facebook, there are a lot of people doing this as hobby income.
Photographer - as stationer, just starting out but great portfolio of non standard shots but also took some standard ones. Kept cost down by not having thousands of shots taken and only ordering the ones we really liked.
Reception I'm a military brat so we were able to use the families club (like a working mans club. Decorations can make an amazing difference to any space. I've known brides use barns, church halls, community centres, empty schools, even an old hospital building!)
Decorations - I got tons of stuff by shopping just after valentines day and getting valentines balloons, napkins, tablecloths, centre pieces... Depending what your style is if there's a time of year that ties in with similar decorations get them just after that occasion. A friend was wanting green in her wedding and shopped just after paddy's day, another friend had pale yellow in mind, shopped just after Easter.
Made my own favours
You've already said about enlisting family and friends, my flower girl her mum made the dress and we said right that's your gift to us then.
Catering - by sgts mess, buffet not sit down. It was cheaper but we did it as we had such a varied combination of dietary requirements, I'm veggie, several other veggies, couple vegans, several allergy sufferers and coeliacs and diabetics and people on heart healthy diets...it was just easier.
Did my own make up and nails (actually my gran helped night before one of my happiest memories)
Hair done by my usual hairdresser, as I was a very regular customer I got a good rate.
Local dj
Wedding night in local hotel, local tourist information were extremely helpful and found us a gorgeous little place that wasn't well known. Four poster bed, beautiful room and we had the place to ourselves!
For the skills based areas some students (hair, make up, graphic design, photography can be extremely talented and happy to get the experience and build their portfolio. My local hairdressing college course students have done some amazing work for charity fashion nights etc. There's also local amateur clubs (eg photography clubs) who are often happy to help if only to advise.
As pps have said think laterally too, I've known brides get their dresses from charity shops, find unusual locations, or just have exactly the wedding they wanted and just because it's a certain style its ended up being cheaper (I'm thinking of a 40's themed one I was involved in, the place cards were ration books!)
You can have a lot of fun with it, there's lots of forum on this too.