Who is getting married? You picked one of the worst months for peonies. If you can wait a month or two, you can buy some from the southern hemisphere. Or try to find stored ones.
Or, if this is for your boss and they want to throw money, get some from places like this:
No one's getting married, it's my sister's birthday tomorrow and she likes peonies. Other flowers would do just as good, but I guess I wanted to buy something nice. And sadly, I'm in Russia and broke, so I can't throw money.
You will not find peonies if your deadline and budget are tight. What does she like about peonies? The color?
I worked for a flower company before (security), maybe I can still remember some.
Or if you do not live in a big city, maybe it is easier to just go to flower shop and check what they have that you can afford.
If you want to save money, buy a few expensive flowers (e.g. Chrysanthemum) and surround them with local grasses and forage flowers. Check around fields or parks near your house. You can at least find some leftover Sage and some tall grasses.
Use these to spruce up your bouquet. It will look impressive without spending 2000+ ₽ on a pure bouquet.