Would you go to Paris and not visit the Eiffel Tower? Would you go to London and not hear Big Ben, or to Rome and not tour the Colosseum? Nor should you go to Venice and not ride on a gondola. YES, gondola rides are unreasonably expensive and every gondolier will quote you a different price, but with a little time, knowledge, and negotiating skill you can take your family on that boat ride and enjoy it without feeling like you've been had with every stroke of the oar.
Hopefully you have more than just a few hours in Venice and can spend some time casually strolling the canals. As you walk around, approach every gondolier and ask his price. Then smile and walk away. He will undoubtably shout after you with a lower price. Listen in on other tourists' conversations with gondoliers and see what they're being offered. Pretty soon you'll have a comfortable idea of a fair price. The price should be quoted per gondola, not per person, and will go up after 7:00 p.m.
Four years ago we paid €65 for a 40 minute ride in mid-summer. I made the guy promise to sing "'O Sole Mio" along the way, too, for no extra charge. Our gondolier was quite charming, and it's been my experience that they usually are. Their English is always very good and they're experts in Venetian history and landmarks. He really impressed my kids by demonstrating some of the tight-space gondola-handling skills these boatmen are tested on during their training and apprenticeships. Our gondola ride through the canals of Venice is a memory we all treasure, and worth the price.