Check with your parks and recreation department. Many parks have covered pavilians that you can get for free or little to nothing. Depending on the time you can get brisket for cheap and cook it and prepare it ahead. Take care w/sandwiches as cost can sometimes be much higher than chicken or brisket or ham. You could provide the meat and ask family to bring the sides desserts drinks, etc.
As far as the wedding goes, check thrift stores for wedding dresses. One near me must have had a bridal salon donate all of their inventory and there were bridesmaid dresses and wedding dresses all for less than $100. My oldest wanted a small wedding. She had her husband to be found a double decker party boat for a song. We had brisket, ham, salad bar w/pasta salad, slaw, 5 bean salad, etc. Beans and bread. The boat was limited to 70. I found small lanterns that held votives for the tables. People changed and swam in the lake for a lot of fun.
My youngest daughter we did a family meal in the back yard as his mother was from out of state. We booked and outdoor facility on a Sunday afternoon for the wedding. Cut the cost by almost 50%. Was cheaper to have them cater and get the facility than to rent the facility and cater myself.
For flowers we purchased the first wedding from Sam's club, the second wedding, our grocery store floral department gave us the best price on the flowers my daughter wanted.
Another way to cut cost is to ask friends if they have access to facilities at a low cost, ie neighborhood association community center, military chapel, pavilion. Also, ask friend about decorations they might have. I bought white tablecloth material on the bolt for $1/yard, white golf tees and used this for aisle runner for wedding. golf tees anchored it to the ground. Used for 2 weddings, then separated later (after washing) and hemmed and gave to daughters for wedding memento.
We also cut bamboo from neighbors yard (w/permission) and used for greenery. Anyway, did each wedding for $3,000 dresses included. People still come up and talk about how much fun they had and how nice the weddings were. If you want to use live flowers on cakes check out edible flowers to make sure what you want to use is not toxic.