If you're not worried about making money and into any niche, then shoot it yourself. You'll have a lot of fun. Expensive fun, but still fun. Unless you can get a girl who is into having her face creamed, you'll find they might want a $1,000. Then finding 3-5 guys who can get off in front of each other and you holding a camera isn't a 100% guaranteed. Will the girl be required to get them ready, will the girl and guys all have recent AIDS tests, do you have the cameras and lights to shoot this. It's not so easy to "retake" the money shots. Location, model releases, IDs, is it allowed in your area, etc are also things you need to consider.
This is a list of things you need to get before you shoot a scene.
Scenario
Performers, guys who can cum to order in a group are not common. Also they need to be able to aim properly. Also make double sure the girl won't recoil as a bunch of strangers cum over her face and into her mouth. A 30 minute scene is ruined as the girl shrieks and runs off when she realises what's going to happen.
Legalities sorted
Health issues sorted
Location, where it doesn't matter if cum doesn't land where it should.
Cameras, will you shoot stills and film?
Lights, with 3-5 men standing around a girl shadows are a bugger.
Robes
Towels
Shower
Shower cream
Antiperspirant
Air freshener
Shampoo
Hair dryer
Mouth wash
Loads of sweet tasting fruit juice. It makes cum taste better, which helps the girl.
Others who have done this will suggest more.
Then editing program, to cut out the bits where you waited for what seemed forever, for the last guy to come. And the bits where the cocks drooped and the guy was tossing away as it got limper and limper.
You may have watched others do this, trust me these are the things you don't see.
Cost. Well if you have all the equipment, shoot from home budget for the girl, guys and the bits and pieces you have to buy in. Your wife if she's not sure about you shooting it, she is certain you won't be using her towels.
Or listen to no nick Frank.