Cheap masterlocks No 1s are easy to come by and a good way to start learning. I got a large supply just by asking friends for locks they've lost the key to.
Lock cylinders from cheap doorknobs are also good ways to start. Kwikset knockoffs (though NOT the Kwikset Smartkey) are cheap and easily available either on Craigslist or the Home Depot. (I found a stash of 10 cylinders + deadbolts on Craigslist for $50.) Home Depot also has a brand called Defiant that's nice b/c they usually have 1 or 2 security pins and are pretty cheap.
Just my thoughts on starting out. Everyone has their own story
