The C3s and C5s aren't much different in price, so if you can fit it, the C5 would probably be a better value. They list new for around $30k, but you should be able to pick a new one up in the mid 20's. A used one will probably cost between $15k-$20k assuming it's not too old and in good condition.
I was worried about fitting a large grand into a room, and the dealer gave me a paper template cut to the size and shape of the piano's footprint. It came in quite handy for seeing how the piano would affect the traffic flow in the room. You could always make one if you can't find a dealer willing to give you one.