If I were to get a parts complete parts kit from M&A parts or Model 1 Sales (in order to build a budget AR-15) what else needs to go into it?

They list that you only need a lower receiver and magazines, do you need any other parts?

Is it difficult to assemble?

Would anyone even recommend one of these budget models?

Here is a description of the parts from the M&A parts site:

Take a look at what is included in a "KIT"....

First, understand what the AR15/M16 is composed of.... 4 basic sub-assemblies:

1) is the LOWER Receiver, the chunk of metal with the serial number- the thing you have to obtain to assemble our M&A Lower Parts kit into. The kit will contain the LOWER PARTS set (LPK). All of the parts that go into the Lower, the lower which you provide.

2) The STOCK which includes the recoil buffer tube, the spring, the buffer itself. If it's a pistol...no stock! Our 16" Carbines come standard with CAR Fiberlite 4 postion stocks, all VARmints and any 18 or 20" come with stad a2 rifle stocks.

3) The Bolt Carrier Assembly (the bolt and carrier) as well as the Charging Handle. (aka: BCA/CH)

4) The BARRELED UPPER (B/U) which includes a barrel, a gas tube and gas block, an upper (either a2 carry handle or a4 flat top - w/ ejection port door cover, fwd assist), handguard.

REMEMBER- Our descriptions are merely "starting points"- nothing is written in stone. It's easy to change out or substitute any component. Just ask.

Put these four sub assemblies together and add magazines, bullets and targets.

A "KIT" includes everything except your stripped lower receiver.

It's that simple. We hear this question about 50 times a day, and we just thought it might be a good idea to try to post it here!

I do believe that all you need is the stripped lower recever, the kit should include all the instructions needed to put it together. If not there are countless sites on the web that give proper instructions in doing such check out www. thehighroad.org these people are a wealth of information and are quite adapt to answering questions. 
Good luck and God speed
edited to add. I don't think you would need specialized tools but the basic armory type punche set and a barrel nut wrench.  I could be rong but most of the tools should be standard

the only problem with a budget build is the budget results...better to budget for a few more months, and build a really good AR.... my suggestion to you would be to, Buy The Damn Lowers Already !!!!! 

2a Go to bravocompanyusa.com and order one of their BCM uppers.  Cheap and truly mil-spec.  As for a lower parts kit, the DPMS is the most common. While on bravo companies website you can also get a bolt carrier group for around $130.  This is, and the upper is where you dont want to skimp.  After that its just your stock and your done.  The lower is really easy to assemble, Waikiki Gun Shop has stripped lowers for as low as $109 right now, hell at that price buy 2, especially when a Noveske stripped lower is almost $200.  Do yourself a favor and buy the complete upper, it will save you from the headache part of the build. 

Building your AR is a great way to learn about your rifle, not only that but youll be better equipped to deal with malfunctions when they occur.  In most cases, youll be able to do a build for under a grand.  Let me know if you need help or suggestions.  I will take a pic of an AR I built almost completely off of bravocompany's website.