This is a spin off reply from your original thread about
How should an amateur photographer charge? but also address this thread.
I can see now you are being concerned whether you have the right gear or adequate equipment for the job, facing with your situation of a possibly low light hotel ballroom with high ceilings, or possibility needing to do wide angle group shots of large group, thus needing more depth of field, thus needing more light or better ISO capability.
Photographers invest in good and often expensive equipment to create better pictures.
Clients invest in good and often expensive photographers to obtain better pictures.
Actually, photographers not just invested in expensive equipment, but also countless hours of practice, training, paid seminars and workshops, trials and errors and learning new knowledge to improve their pictures.
Actually, clients not just invested in photographers but also invested in the support team like makeup artists, assistants, stylists, producers, to improve the pictures they are getting.
If its commercial work, it translate to better viewership, better sales, better branding and better profits for the clients.
If its private work ie weddings, it translate to better documenting of memories of a day where the couple is in the peak of their youth, their looks, young love, the day where so many friends and family gather in attendance just for them, with albums surviving longer than the clients, going into family archives.
In short, photography is valuable. Damn valuable.
If you do not have the backup camera, the proper lenses, then charge your client $80 per hour and use that extra money to rent the proper stuff. Can you now see why you are now worth $80 per hour as suggested by JasonB in your original thread, or even more?
Photographers who own multiple bodies, multiple lenses, multiple flashes, network of assistants, co-shooters, etc, had already upfront put in the money to pay for such expenses, and thus are charging the amount they need to, to keep their business sound, intact and thriving, as pointed out by Catchlights in your original thread.
Just my humble opinion, and my humble efforts in reaffirming the value of photography into the minds of people reading these threads. Both including photographers and clients.