What is the average earnings in a lifetime for a track we place in a library? Like many, I have hundreds of tracks in libraries. Some get placed, many never. Lifetime earnings per song varies from $0, to pennies, to coffee money, to dinner money, to hundreds, and occasionally thousands. But doing the math, you'll see that $150 is not a bad number, especially when it's upfront/guaranteed as opposed to a trickle over 10 years.
Occasionally an indie film makes it big. I recently got a placement whereby the small indie company got bought out by a big one and now it will be distributed to movie theaters. While US writers don't get PRO on movie theater uses (don't ask, it just sucks), we do get paid for overseas theater play. And some will make it to streaming (Amazon, Hulu, Netflix, etc.) which can earn you more money. The one I just got may release a soundtrack album as well. More money for me. We can't expect this often, but the potential is there.
You have a realistic shot at landing that $150 deal whereas when a sync is in the many thousands, the competition is fierce beyond words involving major artists, publishers, lawyers, labels, etc. While some unknown artists like us do earn 10-20K sync deals, your odds are in the teeny weenies. An indie filmmaker doesn't have budget to go after those known artists and that is why they will look to companies like Taxi.
And finally, once you get a deal with that music supervisor, you've started a relationship for life that may gain you more placements. Who knows where that person's career will take them?
So, go after those $150 deals. There is no scoffing at Taxi.

Best,
