Best place to buy stamps for save the dates??

Actually. Amazon and Ebay have stamps sold at discounted rates. Its only really a deal if you have prime otherwise shipping takes away the discount. Ill add a link.Penguin Roll of 100 Additional Ounce Stamps by USPS https://www.amazon.com/dp/B0119U6M6A/ref=cm_sw_r_em_apa_NcRkAbPSGQVS6

No, @Maya, "additional ounce" stamps are not regular stamps, so there is no savings there.

Additional ounce stamps are to add on if your letter is overweight (weighing between) one and two ounces. Its value is only about 21 cents, you can not mail a letter with one.

OP , USPS makes and sells decorative/fun/nicer stamps (aside from the regular flag pattern). You can buy them at the post office or online on the usps website. They all cost $0.49. That's just what stamps cost. Not all post offices carry all designs all the time, so you may have to look around or buy from the post office online, but they will all cost the same, 49 cents.

They only cost more when you go through a third party to create custom designed stamps (though even then, it's the customization you're paying for)

I believe Costco will do a roll of 100 for a slight discount, but don't quote me on that.

We got ours on Amazon so we could pick a pretty design, snowflakes for our winter wedding! It also meant we got them in smaller quantities, so we weren't buying more then we needed.