Saiga conversions are not that hard. Unless you're into having a "name gun" eg "I've got a Krebs!" then its probably worth saving the $550 and doing it yourself!
I've not done a conversion, but I've read the reports of a lot of people who have....
You can get a top of the line FCG (Red Star) for $80. Nice furniture for $50 (or much less if you want). and a feed ramp for $2.
Just move the trigger to the place it normally goes (there's already a hole for it in the reciever), hook up the furniture, move the trigger guard around, and add the feed ramp to allow the old style mags and you're done.
With the furniture and fire control group replaced, your forieign parts are:
Barrel, Trunion, Reciever, Piston, Carrier, Bolt, Mag body, follower and plate. I am not a lawyer, but this would be less than 10 imported parts and your rifle should be legal. Just make sure you use US parts for the furniture and fire control group... and any muzzle break you might add.
I don't know if Krebs uses the Red Star FCG, but if he doesn't not only will you save a lot of money, you'll end up with a better trigger by going this route.
I haven't found a donar Saiga to work on yet, but I'm no gunsmith and this looks like an easy project... look into it if you want to save some money.
EG: IF you bought a Siaga from CDNN for $159, spent $80 on FCG, $50 on furniture and $2 on a feed ramp you'd have spent $292 complete--- half the price of just the conversion from Krebs!