I know, but that's also relative. With Sonos, you usually buy room per room and that way expand your Sonos setup. One Sonos zone with a ZP120 (the zone with the included amp) costs about $500 a piece. CasaTunes offers amps which support "more than one zone" per amp. The cheapest one offers three zones and costs $1499... which, if you do the math, is about the same price as if you would have bought three Sonos ZP120's. Buying more zones gets even cheaper. Eg. An eight-zone + amp costs $3300, which per zone is almost $100 cheaper than Sonos is.

So it's not that much more expensive, it's just that you have to shell out more money at once, but you get more too. I'm actually considering getting rid of my Sonos setup and buying this instead. It's not that I'm not happy with my Sonos setup, quite the contrary. I love it and use it every day. But I'm also thinking that, in the end, CasaTunes will probably be cheaper (in the end I'll need 10 to 12 zones, I've now got two Sonos zones).
Another reason is that this system is fully supported by my home automation system, and it's compatible with other popular systems like Russsound. I've talked to the developer and he says the system is very open towards developers as well. Sonos is very, very closed. They have no API and simply refuse the co-operate with other audio integrators, which is think is a shame and a big mistake.