I germinate my seeds in 3.25-inch square clear plastic orchid pots, so the seedlings grow to expand their roots throughout those pots, and all of my seed medium winds up in the garden soil around the roots of my plants. I use Premier ProMix BX and I add some extra Perlite to it. For my "breeder quality" zinnias I plant just one seed per pot, to avoid having to discard any before first bloom.
If no seed germinates in a pot, I do "re-use" it by planting more seeds in the pot. I re-wash the pots and re-use them from year to year. A standard 11 x 22 inch PermaNest tray holds 18 of the pots. I plant directly into pots to avoid pricking out delicate seedlings from seed starting medium, which if you have a lot of seedlings, can be time consuming. The clear plastic pots let me see the root development, so that I can move the seedling into the garden or re-pot it to a larger pot before it gets too rootbound.
I think I got my first bunch several years ago from rePotMe, and then a year ago I got some more from OrchidNut through Amazon. I don't see that Amazon source anymore. I haven't purchased from this source, but they seem to have them.
They seem to be offering the same pots that I use as:
Part Number: #3.25NCUVM
30¢ each any quantity + shipping
135 shipped anywhere in continental US for $49.00
3.25 inch clear plastic orchid pot with UV inhibitor
(3 1/4 inch square x 3 3/4 deep)
If $49 gets you 135 pots and pays for the shipping, that is a good deal. I might just get some more pots myself. If you needed a lot of those pots, I understand that some sources offer them in case quantities for a good quantity discount. However, you have to watch out when buying pots online, because you can wind up paying more for shipping than pots.
(not associated with any product or vendor mentioned or linked)