My 1st build after EBR disease is a 9mm. I have a RRA mid-length upper on order. I have a lower ready to go I just need to change the hammer to a 9mm and get a mag block. So what is the best cost effective route to go with this? I've heard that VM block with the UZI mags may be good way to go?? Are there any other block that use the cheaper UZI mags? Thoughts?

Quoted: My 1st build after EBR disease is a 9mm. I have a RRA mid-length upper on order. I have a lower ready to go I just need to change the hammer to a 9mm and get a mag block. So what is the best cost effective route to go with this? I've heard that VM block with the UZI mags may be good way to go?? Are there any other block that use the cheaper UZI mags? Thoughts?

VM blocks use unmodified Uzi mags.  "Colt-style" blocks use modified Uzi magazines (including Colt's own-it's based entirely on the Uzi with the exception of the magazine catch).

Now, which one is the "best?"  Good question.  CProducts has opened themselves up to a huge crapstorm by trying to make ONE magazine that works with ALL Colt-pattern 9mms.  They have put tons of resources and probably a million man-hours into the problem and the problem still has the upper hand.

I have a factory Rock River block, and it works fine with both the modified Uzi mags that I got from Rock River and the CProducts magazines I got out of their original product run.  But just like every AR is a world unto itself, with its own foibles and likes/dislikes, every rifle/block combination is unique too.  Decide on a block you like then do a lot of research on it.  In most cases we're talking about a $150 or so part, so it's not trivial, but it's not earth-shattering either.  Try the one you like best and see what happens.  If you don't like it after putting a lot of rounds through it, sell it on the EE and try a different one.

what is the price difference between the modified UZI mag and the regular UZI mag?