I'm guessing it will cost you quite a bit, since ONT is not close to DLR. Have you looked into a shuttle or car service? Those options may end up being less expensive than a taxi. Your hotel may have a deal with a car service or shuttle company, so try calling them, too.
I used to live out near Ontario and trust me when I say it is not close. You'll be better off with the shuttle. With traffic and everything, I'd say even $130 might be low. Another option is to look into hiring a car service. They are usually a bit more than a taxi but flat rate so you'll get a good idea of the relative cost of a taxi.
The shuttles are annoying b/c they eliminate the flat per person rate that you can get at LAX and SNA. instead it's a hefty first person fee, then other passengers.
I destroyed the savings I had found flying into ONT by not checking the transportation costs and finding just what you are finding, that it's NOT cheap. In my case I would have been better off going into SNA or LAX on that trip.
$130 Yea, no thanks. Ontario was SO much cheaper for us to fly into. It was 79 and everything else was over 100! Looks like it will be the shuttle for us. Thanks everyone!