Okay, let's start with "four course dinner." Why is this mandatory? You can have a lovely reception without serving a full meal, let alone four courses. Even dinner receptions I've been two don't have four courses. Schedule the wedding for early afternoon and have a cake and champagne reception. We had a ice cream sundae bar at mine and it was a huge hit. Tables can have a simple centerpice- fresh flowers in a simple vase costs about $7 a table. Placecards are not necessary.
We did not need a big dinner, a band/dancing, etc.
We skipped favors. They are generally something that is a lot of time and effort and going to get thrown away anyway.
Consider your dress budget. Mine was $450. It was the second most expensive thing at the wedding. There is no reason a dress needs to cost 4 figures.
Enlist friends. You are bound to know talented people. My favorite overheard comment at my wedding was my aunt snarking about how my mother "claimed to be doing this on a budget" when my cake "HAD TO have cost $3000.) That amazing cake cost me $250 in ingredients and supplies, paid to a wonderful lady whose labor was her gift.
Flowers are an excellent place to save money by being flexible. I gave the woman who did mine a budget ($200), the color of my bridesmaids dresses (green) and a list of my allergies. She went to the floral market (where the professionals shop) and bought what looked good and was in season. Because of the location and date of my wedding I ended up with an assortment of brilliant colored wildflowers and a stunning visual effect.
We were married in my home church. Mom paid the mandatory "co-ordinator" ($75), the pastor ($200) and the organist (unsure- that was an add on by Mom).
We found a couple who were breaking into the photography business and building a portfolio. For $700 we got them both all day and a written copyright waiver so we could print the digital pictures on our CD ourselves. No jacked up prices on albums, no prints of pictures we didn't really want and no high prices when moms and grandmas wanted extra copies of things. We also had a basket of disposable cameras and our guests took wonderful candids of moments we missed because you just can't be everywhere.
We are not wealthy people. We saw no reason to throw a lavish and expensive party that we really could not afford. Even if we'd HAD $10,000 we would not have spent it on a wedding- it just seems insane to us. Conspicuous consumption is not our cup of tea and we have nobody we feel a need to impress. By "financing someone else's mortgage" I mean that $10,000 is going to go a long way to paying off the mortgage/bills/whatever of the people who drain you of it.
Rethink what you *need* for a wedding. Instead of trying to throw a $20,000 party on $10,000 look at what a reasonable amount of money to spend is and go from there. Discard the "well everybody has..." mentality. Four years later I still have people comparing other weddings they go to to mine and mine always comes out on top. Everyone had a good time. Nobody had to do anything that made them uncomfortable or buy expensive clothes or wear shoes that pinch. Other weddings might be fancier, but I have yet to hear of one that was more fun or happier.