How many packages a day / week?
Forget sets. Look for each piece you need individually (Amazon).
Set up free account with Shippo (or others like it) for buying postage.
Small volume:
Simple kitchen scale is ~$10.
Print labels on regular paper, fold in half, and get free plastic shipping pouches from shipping companies website.
Or you can actually get free label stickers online that go in your printer (but then you need to make sure sizes aren’t getting cut off).
Larger volume:
Cheap USB scale is ~$25.
Label printer is $75-$100+.
Label rolls cost a few dollars (or you can do free method from above).