For starting the seeds, the little plastic trays that come in a pack of cookies or crackers can work well, one more use before recycling. Old school ice trays that have gotten cracked are good for this also.

I try not to spend any money on gardening except for plants and occasional fertilizer.

I've found trading plants a great way to save money. It's usually smaller starts than what one would buy, but for a little over $12, I usually manage to fit about 15+ types of plants in a box. (Quoting the current price for "medium size flat rate box - if it fits, it ships", which seems to come in 2 different forms, although the square inches inside are the same.)

If you're prone to spending money on house plants, many of them travel well.

Overwintering annuals that are really tender perennials is a great way to at least re-allocate one's garden budget, even if the same amount is spent. Having more plants for the same money = worthwhile to me. The stores are not cheated if I only have $$-whatever to spend whether anything survives or not.

Composting one's organic materials is a great way to save on fertilizer and overall number of plants needed. If one's soil is more healthy and fertile, plants perform better/bigger. Along those lines, mulch dry areas to conserve moisture so you don't have to run your hose as much, and contributes to soil tilth as it decomposes.

The less extraneous grass (each their own to be decided) that must be mowed, the less fuel and wear'n'tear of expensive mower or hired service.

Deciduous trees/shrubs placed to provide shade in summer while allowing the rays to provide warmth in winter are a good investment, especially if they are free and all one invests is some sweat and water at first.