good luck the main two suppliers of parts kits are out. now it is down to ds arms new kits which cost more or up to collectors.
the recievers are also hard to find and expensive.
to build one you are in for about 700-1000 to build one. thats w/ all the parts and tools to do it correctly. see if you can find one that is already built.
you are about 1 month behind the supply curve. but if you want more info go to falfiles.com
read for about 3 weeks to a month and make your decisions on what you are going to build form there. that is the best i can do for you.