I setup a cheap auto water system last year. I have it run two hours before I leave for work. That way I can go do a quick check before leaving each morning. I had a failure last year so check every day if you set one up. 1 summer day will kill trees.
I mix my soil though I don't get the prices as low as some on here. I reuse soil from repotting too. Usually mix about half used half new soil. Though I don't have any fancy trees so they don't mind.
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www.americanbonsai.com runs 20% off site wide on black Friday weekend. They also have free shipping on orders over 99$. Not a bad deal. I usually pickup some soil and wire. Good people to buy from any time though. Check them out.
I get free pots throughout the year from building sites. Landscape people don't always let me have their empty pots but it never hurts to ask. You just need one or two big scores and you are set. I cut the pots down to the size I need and use some window screen to cover the large drainage holes.
Watch for sales at locally owned garden and landscape places. Sometimes they have piles of old plastic pots they would be willing to sell.
I get small 4-5 inch pots from Amazon. 100 of them run about $20. Last me a couple years and good for seedlings.
Some Home Depot's have reject or damaged wood that is 70% off. I hit one every week to see if there is anything I can use.
Think outside the box and have fun!