I use cloudmade on one of my website, this is how i use their tiles :
L.tileLayer('http://{s}.tile.cloudmade.com/{your_key}/{style_id}/256/{z}/{x}/{y}.png', {
attribution: 'Map data © 2011 OpenStreetMap contributors, Imagery © 2012 CloudMade'
}).addTo(map);
Key and style are directly in the url, you might want to use the basic cloudmade style, id is 1
.
And yes, cloudmade is turning off their service for small users, but it's not effective now, may 1st so your map should work.