The information here is general in nature. There are many different kinds of deals for shows, and your own circumstances may be different.
There are a few different ways opening acts are paid, and much of what determines what kind of deal you get depends on what kind of show you are playing:
- At larger shows (be they larger club shows or shows in even bigger venues), there is usually a set fee for an opening act. This fee can be A LOT smaller than what the headliner makes. There is usually an unwritten norm for opening act fee in most areas - say $100 - ask around and get some feel for what others in your town are getting.
- At small club shows in which the headlining band has a door split deal, the opening act may not get paid at all. In these cases, some kind promoters will throw a little money in the direction of the support band if the show is a big money maker or the headlining act might pay you a little something. Another scenario is that the opener will get a portion of the door split. With this kind of show, it is very important to go into the show knowing what to expect. Don't assume that you're simply getting a cut.
- At very large shows in which the gig represents a major promotional opportunity for the supporting act, again, things can vary widely. The opener might get a small set fee. The idea here sometimes is that the promotional benefit of the show is payment enough. In fact, in some instances, opening acts "buy on" to large tours, which means they pay a fee for the chance to be a support act. Although this happens, you should never commit to this kind of deal without having the advice of an agent or manager. This kind of deal is also not for you if you are not in a position to take advantage of any buzz generated by your shows - for instance, having distribution for your music is a must to get the benefits of a buy on tour.
That doesn't mean, however, that you should accept any opening offer slot that comes your way. Although they are good promotional opportunities, you should weigh up the expense of playing the gig with the benefit you will get from it - for instance, if you have an indie rock band, it's not worthwhile to travel 500 miles to support a hip hop act. Also, especially if you're not getting paid, make sure you will be allowed to sell merchandise at the show. Some headliners don't want the opening band to sell merch since it could distract from the sales of their items. This is less of a problem at a small show, and a very big deal at large shows. If you can, try to get in on some rider action, and try to keep your costs down by sharing gear with the headlining band (this may be harder to arrange when we're talking about a major act with an elaborate stage set up).