I am going crazy searching for the right song for my film..There is a dance sequence that needs to be choreographed..
She likes Celine Dion, Annie Lennox, Mariah Carey, Christina Aguilera. That type of music - pop/rock with a crescendo-type of singing. One that starts slow and builds up with the voice increasing in pitch and then crashes down..It needs to have changes in tempo as well..

Something orchestral with a song set to it..

That would lend well to a passionate contemporary dance about 2 people falling in love and out of it..

I find tons of music - some is quite decent. But its a lot harder to find good songs - hard to get a good singer..

Are there any recommendations ? I am willing to pay but not tens of thousands of dollars of course..

I am going crazy searching for the right song for my film..There is a dance sequence that needs to be choreographed..
She likes Celine Dion, Annie Lennox, Mariah Carey, Christina Aguilera. That type of music - pop/rock with a crescendo-type of singing.
....

Are there any recommendations ? I am willing to pay but not tens of thousands of dollars of course..

You might want to try local bands. You can usually get them to let you use their music in your project for free as long as they retain the rights to the music. It's a win-win usually for the band.

Since you're in Sydney you should have access to a lot of local bands.

Wayne