Here's the height per rack, I measured the depth to be 70cm as well as 50 cm wide for these racks.
http://i.imgur.com/vNtSYh5l.jpgOk so lets say if your talking 10 Avalons, roughly 170 CM high, plus 1u additional, maybe a roundup to 5cm per space x 10 avalons 35-37 racks. Oh and yes the prices on the website are per month, I will ask our hosting sales guy what he would offer for a 10 stack of avalons, will let you know when I hear back.
Edit: Hmm looking closer again, 4.5cm per rack seems to be what we should be going by..