I just moved to a new house so my personal resources are very limited. Luckily there is a mushroom farm close by that sells an entire pickup load of mushroom compost for $20 and I am having very good luck with equal parts perlite, coconut coir and the compost, it comes out as a very loose starting mix. It is working well for the seedling starts and as potting soil once my sprouts have true leaves.
For the poster who said they have a hard time sowing seeds in a row because they use plastic trays try moving to larger wooden boxes made from scrap wood mine are 14" x 20" x (3" and 6" Height). They are large enough to separate the varieties by about an inch and do not collapse catastrophically. As the sprouts get larger I move the best looking ones to the deeper boxes or to individual pots / solo cups. Try to keep the roots from bottoming out in your seedling containers, it has a tendency to send many into bloom which slows their growth once out in the garden. When plants are putting energy into reproduction they stop putting energy into growth. This is one of the reasons many people prefer to plant directly in the garden for the faster growing plants.