C&Cs don't have to look cheap!
For the bottom, if you buy a piggy bedspread (or sew one yourself) that covers the outside of the coroplast too, you can't tell that the bottom is coroplast because it's just covered by fleece! (And you could do whatever colours suit your house best) and if you don't like the connectors looking cheap with the grids, you can Zip-tie them together, one small zip on the top and bottom corners of each grid, (You can buy zip ties in different colours to match the grids), cut off the excess and you can't even see them!
I have also heard of people spray-painting their grids to a colour that they liked best. I didn't hear how well that worked out for them, but as long as your piggy isn't one who likes to chew on anything and everything, you could spray the grids to match your furniture!
I have seen cages looking nicer with the wire-closet shelving used for sides, it looks very neat and uniform with the coroplast still as a bottom. I know there are a few like that in the gallery!
For my cage since I'm using fleece only and not loose bedding, I opted to have 3" sides instead of 6" sides for the coroplast, which looks a lot better. (And lets the piggies see what's going on without having to stretch their little heads above the sides!)
I wish you the best of luck in designing a cage that works for both you and your piggies!