Have you considered building one in? Our shower is 4x5 and that's what we did. Looking at the prices you've posted it appears it was a more economical way of going about it too. I'm not sure about the advantages or disadvantages though becaus buying a prefab pan is something we didn't consider.

We are tiling the walls and considered tiling the shower floor too but I was hoping for no grout etc. PLus I like the look of a solid surface pan.

We are in the process of finishing a new bath and chose the Onyx instead of tile because of the grout issue with tile. We got the low profile and it is installed, but shower isn't yet finished. It looks great and our HB has used this product a lot and highly recommended it. The color samples online are not true. We picked the color from sample chip.

Good luck!

I didn't get too much feedback, so thought I'd ask again. We pretty much have it narrowed down to Onyx collection or KBRS aka showerbase2. Onyx is molded as one piece. KBRS is 1/8 inch solid surface acrylic laminated to another material. We kind of like the look of the KBRS pan better, but are wondering about possibility of less durability in the long term due to the lamination.

We have the krbs pan, but opted for corian rather than the acrylic. It has only been installed a year but so far no issues. I think the adhesives they use will last as long as the material itself. It looks fantastic - not like a shower base at all but like a floor.

I don't have any great pics but here is one before the tile was grouted and base was cleaned up:

and here is a partial after the shower was done:

I bought the corian bench top and niche shelf from them too, it was only like $60 - a fraction of the cost of stone.

Have you considered looking at one of these? Formed corian shower base?

Here is a link that might be useful: Formed Corian Showerbases