Yes, Sir. Piecing it together with junk yard parts is possible, as long as you are able to find everything. It could possibly be a little bit cheaper than a basic kit once you have refurbished everything, depending on what you have to pay for parts, turning rotors etc. Still, paying another maybe $50-100 to get a complete kit with all new parts is well worth it, IMO.JMHO. Been there. I think Olle will tell you the same thing.
Of course, you can do it cheaper by using the junk yard parts as they are (done that too) but you usually end up doing the job two, three times over if they don't work. And putting brake parts in unknown condition on your car kinda defeats the whole purpose.
Just for the record: I actually tried to find used parts for my latest conversion, but couldn't find any locally. If you have to order parts and have them shipped, I can almost promise you that you won't save a dime.