Like quality downhill mountain bikes, quality manufactured freestyle (peg) bikes are expensive. The price point often excludes the young and cash-poor from skibiking as a sport. Right now, I look at that as a good thing.
One way bikers get around the expense is by building homebuilt ones from bicycle frames they can find.
Most ski resorts in Colorado outright ban homebuilt bikes. Smart risk management almost dictates this. There are many reasons why.
Most people are not professional bike builders much less skibike builders. You never know what someone will cobble together in their garage or backyard. I've seen the stupidest builds show up - and the end results.
Adventurous bikers soon discover how fun jumping can be. The frame however must be built to withstand the impacts of landing those jumps. Amateur builders rarely take this into consideration.
Most bicycle frame welds are not meant to withstand the impact of jumps. At one large well-known Colorado ski resort they started having homebuilt bikes explode on impact off large jumps in the terrain park. People got hurt.
The connection of the bike frame to the skis can also be pretty sketchy on homebuilt bikes. I've seen homebuilds just fall apart on an average ski trail. People will just cobble anything together without thinking of safety and consequences.
Loading and carrying a homebuilt bike on a chairlift can sometimes prove to be challenge too. Professionally manufactured bikes are meant to be loaded and carried on the chairlift.
Homebuilt are great for riding in the backyard or community sledding hill. They have no place at a commercial ski resort.
There are a variety of professional builders in the USA. There are a variety of skibike manufacturers in Europe too. A variety of economically priced new and used bikes can be purchased at SkiBikeFun.com.
If you are thinking about allowing skibikes at your ski resort, think about the level of risk you're willing to accept before permitting homebuilt skibikes.