Wishing Well Engagement Party

I am hosting an engagement party for my cousin and due to lack of funds for the wedding they would like to have a wishing well engagement party. Is that tacky? Is it okay to place a card in the invitation that states:

Soon you will hear our wedding bells,
As friends and family join to wish us well.
A WISHING WELL ENGAGEMENT PARTY was thought to be great,
But only if you wish to participate.
A gift of money is placed in the well,
Then make a wish .... But shhh don`t tell!
And in return for your kindness, we`re sure
That one day soon you will get what you wished for.
But more important we ask of you,
Your prayers of love and blessings too!

If it is, how can I restate the poem in order to let the guest know to bring money. A lot of them won`t understand the "wishing well" concept