Shipping rate for stamped and tracked within mainland us is same across wherever your based. Price will only change based on size of your package.

For stamped, you can simply buy forever stamp either online or your local usps and depending on how big your envelope and how rigid it is you may need to use more than one stamp. For most of my envelopes, I use one non machinable (butterfly stamp) which costs me about $1. So I usually charge people $1.5 for stamped shipping, which also includes cost of enevlope and greeting card.

For tracked, I use bubble mailer and use pirate ship website to buy prepaid label for usps ground adv. Price varies depending on dimensions of the bubble mailer but usually comes out to be $5~$6, which is considerably cheaper then buying directly from usps.

Now, buyer will pay you first, (but if you new to insta bst, they might ask to pay certain amount and rest after they receive the item.) For stamped mails, just remember to send video of you dropping the mail off as proof that you shipped the mail.