A great way to save money AND ensure your seedlings get off to a great start is to make your own indoor seed starting mix.
Recipe:
4 parts screened compost (screened or "filtered" compost free from twigs or large chunks)
1 part vermiculite
1 part perlite
2 parts coconut coir
to make mixing easier, make sure ingredients are lightly moist.
This mix strikes a balance between moisture retention and drainage, both of which are necessary for seedlings.
Happy planting!