Advertising an afterparty of a popular event - how to value the ads?

Hi guys,

I'm very new to all this digital marketing stuff and looking for some advice.

I own a website, facebook page and facebook event for a Finnish beer floating summer festival. It's basically an informational website about this event in Finland, where thousands of people flow down a river in inflatable dinghies whilst drinking beer.

There will be over 5000 people participating in the festival and all the information regarding this event is distributed via the 3 channels that I own (website, fb page, fb event). I am estimating that my website will get around 10,000 visitors per month on the months preceeding the event and a total number of participants close to 10,000 for my facebook event as well.

Every year, various night clubs in Helsinki claim to have "the official" after party for the Kaljakellunta event. Although I'm not an organiser, I am pretty much in the position to decide where the "official" after party will be, as I own all the marketing channels.

So I'm thinking I could sell a nightclub the following package:
-Announcing that their night club will be the venue for the official after party of the event
-Placing a large ad on my website to promote the night club and after party
-Promote the after party via the facebook event and page.

Now I have absolutely no idea that how much value this package would create for a nightclub. Thousands of people must mean a lot of revenue for them, especially considering the prices of basic drinks in Finland (5-10€ each) and similar prices for entry. I would be pretty much able to direct all participants into one night club so it must be worth quite a lot I think?

I don't know at all how I could value this "package" and sell to them, so I'm looking for some advice from you pro's

Thanks in advance.