Best WLAN speakers for openHAB and Alexa?

I’d like to set up a multiroom speaker system that can be addressed by openHAB2 (for TTS mostly) and by Alexa as well. It should be possible to address each speaker individually.

So far, Sonos seems to be the only choice - but it’s not an option for me due to the high price.

Chromecast Audio can bind to openHAB, but not to alexa.

Are there any other alternatives?

Yes, Sonos Players are expensive, however due to the new Sonos One (Play 1 with included Echo) the price for the “old” Play 1 is actually falling (154€ incl S&H in DEU ). I’m ready to buy the last needed.

Alexa can bind to openHAB so if Chromecast Audio can bind to openHAB can’t you just glue the two together inside OH with your own rules?

In my setup I’ve declared a handful of items that are published to Alexa and only bound them to Alexa I then have rules that map them across to other items that do the work. Most of the time it’s a one to one mapping i.e. an Alexa Switch to a Light Switch and a generic rule keeps all those in sync. But sometimes I’ve got other functionality going on i.e. Alexa turn on Bedtime carries a time delay before passing it on to the business logic enabled Bedtime Item so I have a chance to get to bed before the security system activates.

Did you look at the sonos predecessors squeezebox? there is an OH2 binding for it available and you can run the server and the players all on raspberries; Running it for years and it works very well for my needs.
Can recommend (at least that is what I use on 5 raspberries) for easy installation and easy config (incl. write protection that vastly enhances the life of the SD card); one catch though, squeezebox is a product that is at the end of its lifetime