I believe that you would need a Semi-Auto. Kit to be sure that you are legal. These cost closer to $500 than the $165 that SMG kits cost.
You can buy a complete (Pre-Welded) Receiver, including IMI Receivers. THese cost more (Close to $300) than unwelded which usually run $40 - $100.
But, I believe that some of the pre-welded receivers are named Pre-Bans. You will definitely wish to check into that. As for myself, I would not build an Uzi unless it was Pre-Ban. It just makes no sense to me at least to have an Uzi with fixed stock. It just looks wierd. If you were to fix the orignal stock it would look OK, but it won't fold.
I believe that Pre-Ban Uzis are not that much more than Post-Bans. So, it shouldn't be a big cost difference. ANother note is that Semi-Uzis run around $1,000 while FA Uzis run around $3,000. But, I have seen a Registered Bolt (conversion part ???) for $1800.
Of course, this all depends on what you want. Basically is what I am saying is that for about the same thing you can build a Post-Ban, get a Pre-Ban, or for several hundred more get a legal FA Uzi.
[Edited to note that I just noticed that you are MO and an Uzi is not a C&R.]