Crack in shower stall floor
That looks like fiberglass (if it feels pretty flexible its fiberglass, if it pings when you tap it with your wedding ring its porcelain) which could in theory be patched with a fiberglass resin patch. Use the kind with the fiberglass mesh, not just Bondo it will crack. Or you could try West Systems G/Flex Epoxy Kit WSY-650K, I've used it to do some hairy fixes and it is pretty impressive. Having said that, I would consider any patch to be a temporary fix at best. You've got water, regular stressing forces caused by your shifting weight in the tub, and a hole that may be leaking into an area that you can't see. Bad juju.  Also, and I hate to be the bearer of bad news, but the last time I replaced a shower/tub insert it ended up costing the homeowner about $2300 because we had to tear up and replace a lot of the sub-floor due to years of minor leaks and overflows. You may not be looking at water damage yet but I wouldn't be surprised if you have to perform a little surgery once that shell is out. 
Best of luck,
ph