The process basically works like this:
1. Check your state laws to make sure that you can own a machinegun.
2. Call your chief law enforcement officer (CLEO) and see if he will sign off on a Form 4 transfer. If he doesn't, you may need to go the trust/Corp/LLC route.
3. Find the machinegun you intend on purchasing and buy it. If in state, you will need to coordinate the transfer through an NFA dealer; if out of state, this will need to be coordinated using two NFA dealers.
4. Following purchase (you give seller the money) the seller delivers the gun to the NFA dealer to hold pending approval of your Form 4 by BATFE. If gun is out of state, this may require involving two NFA dealers and two transfer fees
5. Fill out Form 4, get passport photo, get finger print cards completed.
6. Get CLEO to sign off on your Form 4 - may require additional local background check.
7. Submit Form 4, photo, fingerprints $200 and CLEO signed Form 4 to BATFE.
8. Wait for 3-4 months for ATF/FBI Background check/processing.
9. When you get your Form 4 back with the tax stamp, take it to your NFA dealer and pick up gun.
I find that the folks on Sturmgwewhr.com are quite savoy about current machinegun prices. I'd simply post a question on their NFA board asking about the price range for the gun you are looking to purchase - provide good details on exactly what you would be purchasing and condition.