You have to be a little careful with envelopes-the automatic machines in the post office can crush seeds. The big envelopes with bubble wrap incorporated into the envelope can work for small seeds. I have had seeds crushed in the mail.
Right now a small flat rate box is $6.80, and you can fit tons of seeds in it.
For those of you near the Host DND who is in Michigan- the USPS also has a regional rate postage which is a little less, but they don't advertise it and it's a bit hard to find out about, you might ask at your local P.O. when you go to get the little flat rate box. My local postal worker told me about it when I mailed something to a nearby city in a medium flat rate box- she said it would have been cheaper. The flat rate boxes are free, then you pay the postage when you mail it. I am not sure if the regional box uses the same flat rate box or not.
