It's like crack you see...
The first rounds are cheap. Someone might even pay for you. You think they're doing you a favor. Pretty soon, you find yourself plunking down the money for a new choke tube. After that, you move from cheap Value-Pack #8s to more expensive AA or STS #9s.
Before you know it, you decide that you've got to upgrade from your old pump-gun. You get an auto, maybe a slightly-used 1100. That works for a while, but you want more... you need more. You're within a couple targets of running a straight, but can't quite get there.
Maybe an O/U would help. You get that, and with a few thousand shells worth of practice, you can start to run 'em clean now and again. It might be fun to do some competitions. There are some nearby, and the entry fees aren't too high.
After a few, you decide that since you're already going to the competitions, you may as well shoot as much as possible. You order some sub-gauge tubes for your O/U. Darn, those small shells get expensive. You'd better start reloading. Pretty soon, you've put an addition on the house so you have somewhere to store your array of MEC machines.
Now that you've got that much money sunk into it, you better do a lot of shooting to justify yourself, so you travel far and wide to go to tournaments. You start to understand that the actual prize purses are only a small amount of the money that trades hands during the weekend. Pretty soon, a trip to Las Vegas seems almost anti-climactic.
At some point in there, you may have lost your day job, your wife, or both. Not that you'd notice or anything....
So, that's what it costs to shoot skeet. **
Unless you were asking how much a round costs, then it's anywhere from $3 to $5.
** BTW, it isn't only skeet. Some variation on this progression can be applied to virtually any competetive sport.