5 grand can get you a HK94 all day long. Pay for the tax stamp and have the barrel cut and re-crowned.

You can get a SP89 for about the same price, give or take a few hundred....it's registered as a handgun, so no tax stamp needed.

They're both less money than a real MP5 and probably well within your budget. You can get both and save 8 grand over a MP5...

 

What about a Model 37 Ithaca
Find a parkerized police model not a blued field model....its a riot shotgun @ minimum barrel length with a chrome bore and a maximum magazine length. They are slam fire guns.
Why spend 5 grand on a semi auto????

 

A Class III dealer friend of mine still had some MAC10's in .45 a couple months ago, and some other militaty armaments. PM me and I'll find out what he's got left.