There are a bunch of free things that you can take advantage of for your garden!
Coffee Grounds
You can get free coffee grounds from Starbucks or another local coffee shop. Coffee grounds make an excellent fertilizer and are great for compost. You can also use used coffee grounds as insect repellent. Starbucks has a program where they put out used coffee grounds for your garden in a tin labeled in their store.
Wood Chips
Call your local tree removal company, arborist, visit ChipDrop, look for a Facebook group advertising free wood chips, or look on Craigslist. Companies will deliver wood chips to your driveway for free that they would otherwise pay to get rid of at the dump. It is important to know that typical loads can be up to 10 or 20 yards. Wood chips are excellent at preventing weeds and make an attractive and natural ground cover.
Wood Pallets
These can be great for building a compost bin, garden furniture, raised beds, etc. They are often advertised on Craigslist. Many businesses have them such as home improvement or grocery stores.
Plants
Check FreeCycle, NextDoor, Facebook Marketplace, or another app that has a plants and free stuff section. Join a local garden related group: sometimes they give out freebies. Ask family, friends or neighbors for plant starts.
Seeds
Check to see if your library has a Seed Library. They might have a station filled with seed packets.
There are companies that mail out free seeds for your garden. Save Our Monarchs is offering a Pollinator Garden Seed Mix here with a $1 shipping cost. Live Monarch offers free Milkweed seeds when you mail them a self addressed and stamped envelope here.
There are seed exchanges such as Seed Savers Exchange, Garden.org and Houzz. And Facebook seed swap groups and reddit.com/r/seedswap. You could also save seeds from last year.
Compost
Use your kitchen scraps, leaves, and grass clippings to make compost. Add some coffee grounds to attract the worms.
Happy Gardening!