I live outside Vancouver, BC, Canada and in our whole large metropolitan area there is only one manufacturer of cultured marble. I have ordered for two bathrooms from him, and though he is a great guy and makes a lovely product, I feel I have to pay a premium because he has no competition. I would google search, yellow page search and then even check Lowes or Walmart or HD or any large home hardware store. I think there are far more choices in the US. Because you are looking for a fairly standard size, you may be able to buy stock and not have to have it custom made, thereby saving some money. On the other hand, the advantage of custom is that they can make it exactly the way you want it, For my current Master BR reno I had a 3' X 5' shower base made in a BM colour to match perfectly with my colours. In my basement I chose a very subtle white on white pattern and had them finish it in a matte finish, so it doesn't look plasticy at all. I have had many compliments on it from guests! Again, since it was custom made, I had them make an 8" deep shelf along one wall (It actually extends 10', the entire length of the room). That shelf is one of my favourite features in the whole BR!

If I "ignore" the issue, and just caulk over the crack, what's the worst that could happen? Second worst: Water leaks behind the caulk, destroys the studs behind the tile and the joists in the floor, and you have to rip out the whole shower stall, wall and floor and replace everything. And do mold remediation. Worst: Water leaks in there, destroys the studs behind the tile and the joists in the floor, and you step in the shower one morning and the joists give way and you and the shower stall end up in the basement. No fooling, this happened to a friend ... he caulked around the base of a leaky toilet because he didn't want to have to remove/replace toilet and fix the problem. About a year later he sat on the toilet and ended up in the basement because the joists had rotted. The paramedics were amused.

How often does your power go out? Adults and teens in the house should be cognizant that when the power does go out, the half hour shower will have to be postponed but it's not like it has to be an overriding fear that prevents the bathroom from being used. Commercial and institutional buildings with basement restrooms often have the same setup, albeit larger systems. My laundry tub, washer and basement bath all go into the same ejector pump pit. My power typically will only go out due to a severe thunderstorm and be out for 4 to 6 hours tops. It's pretty obvious that the power is out and the basement bath, washer and laundry tub are just not used at those times. The toilet is older and has a 3.5 gallon flush. If the pump has just cycled, It takes 2 flushes for it to kick in again. My guess is it would take at least 5 or 6 flushes to start coming out of the shower drain. Maybe more - I've never tested it. The pit doesn't fill to the top before the pump kicks in; there is some buffer there as well.

Heed MillWorkman's advice. Any change of plane, whether it is wall to ceiling, wall to floor, wall to wall, etc.. will almost always require caulk of some sort. !00% silicone for anything around water. In other areas, a siliconized caulk, or paintable 100% silicone caulk can be used. I have done a lot of painting, either for myself or others, and I learned from an experienced pro to put a light layer of caulk in corners, around mill work, and wall to wall/ceiling/floors to prevent the paint from cracking/splitting. Just my 2 Lincolns worth.