That's such a subjective question. Where I'm from, Clif Bars, PowerBars, etc. cost about $1 each. Bars tend to have more calories than gels, so you tend to get more for your money in that sense.
But gels offer their own advantages that may make them worth the money for you. As noted, some people see them as more convenient. Others find them easier on their stomachs than solid food. You should try a few for yourself to see if these advantages are true for you. Then it's up to you to decide if those advantages are worth the money.
One final note is that if the longer the ride, the more issues your stomach may give you. This is when having a wide variety of foods becomes very important. If you get to the point where you can't force yourself to down any solid food, a gel will definitely be worth the money if you're able to force it down.