For my friend Kate's birthday last year, I hired a singing pink gorilla. I wouldn't recommend the place I got it from because the gorilla was not giant, as advertised. In fact, the gorilla stood just about 5 foot 5, shorter than most of the ladies at the event. She was also about an hour early to the party, arriving shortly after we did, which was quite awkward.
If you do want to hire a gorilla, an Elvis, or a singing telegram of any sort, you can just search the web. You'll be surprised by the variety of options.
My friend was amused at the time, though later, when I brought up the gorilla, she said, "Oh, I thought that was a monster!" I could see how she could be confused.
I was a little surprised when the gorilla asked if I could hold her car keys, before she began her dance number. Not the most professional of primates.
The gorilla did a song and dance routine (in a grating, Long Island accent... where did they get this tiny lady?!)
One of the most memorable songs was very creative and apropos, "you're the greatest 32 year old in the world, the greatest 32 year old in the world!!!"
It only cost about $100 to hire the monster, which included a bottle of champagne and a bouquet of balloons.
In the end, it was a fun experience, perhaps made even more memorable by how very, very strange it turned out to be.