A few MAK 90s were sold with the threaded muzzle, and it is generally held that these guns were in the pipeline as AKs, and were converted after the Bush Chinese Import Ban went into effect. I have seen a few of these, legitimately NIB with receipts, etc., come out of the woodwork recently. The going rate for MAK 90s in my area is $350, and $400-$425 for NIB with all the accessories. 30 rd mags can be found for $6 ea. on up depending on condition and quantity bought.
That is not a particularly good deal, IMO.
Also, if you have any thoughts of converting it to pistol grip config, then you need 4 US parts. A US stock set with pistol grip would count as three (upper and lower HG count as one part) and you would need like a US hammer or trigger or mag followers or floorplates to make up the additional part. So adding for all that, it is at least another $100, and now you've paid $500 for what $300-$350 would buy in a Romanian SAR-1. I won't debate which is "better", I am just comparing two stamped receiver AKs with like features.
If he won't flex on the price, I'd walk.
Noah