If Just going to visit Azar Goshnasp, The Tekab road is better & safe & less expensive but linger.
To Takab is possible by bus then Taxi for another 42km to Azar Goshnasp.
Another possible path is Zanjan-Dandi-Azar Goshnasp, this one is mountainous & need rental car.
I've indicated the akab road in light green on map.
I took taxi from here to Takht-e Soleyman for IR450,000 (May 2008). It takes good 2 hours one way and the ride is very scenic with strolling hills. Along the way, the taxi passed by Dandy, which is about 1 hour from Zanjan and 1 hour before Takht-e Soleyman. There is nothing much to see in Dandy. You need at least 1 hour to stay in Takht-e Soleyman. Admission IR4,000 (May 2008). Taxis are waiting at Ferdosi St and Beheshti (Khayyam) St.
On my way back, the taxi drive drove around the region, firstly to Takab, 30 mins further from Takht-e Soleyman. Then it picked up a passenger and route to Bijar (about 40 mins from Takab) before going back to Zanjan, another 1.5 hours. I enjoyed the scenic trip as I could see more things and landscape.