I'm new to the AR15 world, but I'd like to buy a complete Mega Lower with a fixed CAR stock ($199)and mate it with a complete Model 1 Sales 16" Post-Ban M4 CAR Upper Half ($455.00). Does anyone have experiance with these products and companies? The total price would be $654. Can I buy or build a better rifle for that price or less with some other companies parts?

I've never heard anyone say anything bad about the Mega lowers...I've got 2 model 1 kit guns, and there were issues with one of them, but model 1 made it right with no trouble.  

Both rifles shoot great, and I'm happy with them.  I used Eagle lowers from Quantico Arms, which is only about an hour away, so I got them direct.  

I think you'll be happy with the combo you are planning; just bear in mind that Model 1 is a "no frills" kind of kit...the small parts arent' gonna be as good as a DPMS kit, for example.  You may have to trim some springs, stuff like that.  

Bear in mind the model 1 kit will come with the buttstock of your choice, and all the lower receiver pieces.  Don't pay extra to get a complete lower, 'cos then you'll have an extra buttstock assembly laying around, which will almost certainly turn into another rifle by some sort of weird voodoo hehehe.  Ask me how I know!

Buying just the stripped Mega lower saves you $100, which you can put towards something else, like optics, or whatever.  Also, I'd recommend a flat top, since the optics options are so much better down the road.  That does mean you'll have to get some sort of sight, though, so the $100 you save will go right back out the door.