When starting seeds for the summer garden I planted seeds in cardboard egg cartons. These are free. I love free and can be cut into sections and be planted directly into a larger pot or into the garden. Since I start so early I transfer the plants to a larger pot and then later into the garden.
Next I put the egg cartons in a plastic container and cover it with a clear sack from the dry cleaners, in a clear plastic disposable lettuce container with a lid or a clear shoe box storage container. It needs to be covered to keep the moisture in and create a greenhouse effect. Even covered it will probably need to be watered occasionally. I use an repurposed dish soap container to water. It is gentle on the young sprouts and less likely to knock them down than pouring water on them. Next I put them on top of the freezer where the defrost cycle keeps it nice and warm. That way I don’t have to spend money on a warming pad or electricity to run it. Most seeds do not need light to sprout.
Once they are sprouted I move them to the light box the wonderful hubby built for me out of lumbar scraps (gotta be frugal). It can be seen in the above photo. It is enclosed on the top and three sides. I lined it with foil to help reflect more light. It is open on the front for watering and to allow ambient light in. When the plants are small I place the containers on a box to bring them closer to the light. As they grow I go to a smaller box. Once they are big enough I move them to a wire shelving unit with a fluorescent light attached and set it In a south window so the plants also get sunlight. Once the box is empty I move the next batch of sprouts into it.
These are lettuce and tomatoes I started in January. I will be able to move them to the unheated greenhouse in a few weeks.